Merged few patches into one patch and fixed for Waterfox
Original authors of patch for Firefox:
Wolfgang Rosenauer <wolfgang@rosenauer.org>
Lubos Lunak <lunak@suse.com>
Original patches => http://www.rosenauer.org/hg/mozilla/file/firefox68

diff --git a/browser/base/jar.mn b/browser/base/jar.mn
index 8e532437277a..dbe8aa705929 100644
--- a/browser/base/jar.mn
+++ b/browser/base/jar.mn
@@ -33,6 +33,8 @@ browser.jar:
 #else
 *       content/browser/browser.xul                   (content/browser.xul)
 #endif
+*       content/browser/browser-kde.xul               (content/browser-kde.xul)
+%       override chrome://browser/content/browser.xul chrome://browser/content/browser-kde.xul desktop=kde
         content/browser/browser-addons.js             (content/browser-addons.js)
         content/browser/browser-allTabsMenu.js        (content/browser-allTabsMenu.js)
         content/browser/browser-captivePortal.js      (content/browser-captivePortal.js)
diff --git a/browser/components/preferences/in-content-all-new/main.js b/browser/components/preferences/in-content-all-new/main.js
index 226b9df1dcbc..a747540c1d72 100644
--- a/browser/components/preferences/in-content-all-new/main.js
+++ b/browser/components/preferences/in-content-all-new/main.js
@@ -148,6 +148,13 @@ var gMainPane = {
       }, backoffTimes[this._backoffIndex]);
     }
 
+    var env = Components.classes["@mozilla.org/process/environment;1"]
+      .getService(Components.interfaces.nsIEnvironment);
+    var kde_session = 0;
+    if (env.get('KDE_FULL_SESSION') == "true") {
+      kde_session = 1;
+    }
+
     if (Services.prefs.getBoolPref("intl.multilingual.enabled")) {
       gMainPane.initBrowserLocale();
     }
@@ -542,6 +549,17 @@ var gMainPane = {
       }
       try {
         shellSvc.setDefaultBrowser(true, false);
+        if (kde_session == 1) {
+          var shellObj = Components.classes["@mozilla.org/file/local;1"]
+            .createInstance(Components.interfaces.nsILocalFile);
+          shellObj.initWithPath("/usr/bin/kwriteconfig");
+          var process = Components.classes["@mozilla.org/process/util;1"]
+            .createInstance(Components.interfaces.nsIProcess);
+          process.init(shellObj);
+          var args = ["--file", "kdeglobals", "--group", "General", "--key",
+              "BrowserApplication", "waterfox-current"];
+          process.run(false, args, args.length);
+        }
       } catch (ex) {
         Cu.reportError(ex);
         return;
diff --git a/browser/components/preferences/in-content/main.js b/browser/components/preferences/in-content/main.js
index 947e8b4a8060..4130ba0ce326 100644
--- a/browser/components/preferences/in-content/main.js
+++ b/browser/components/preferences/in-content/main.js
@@ -363,6 +363,13 @@ var gMainPane = {
       }, backoffTimes[this._backoffIndex]);
     }
 
+    var env = Components.classes["@mozilla.org/process/environment;1"]
+      .getService(Components.interfaces.nsIEnvironment);
+    var kde_session = 0;
+    if (env.get('KDE_FULL_SESSION') == "true") {
+      kde_session = 1;
+    }
+
     this.initBrowserContainers();
     this.buildContentProcessCountMenuList();
 
@@ -1162,6 +1169,17 @@ var gMainPane = {
       }
       try {
         shellSvc.setDefaultBrowser(true, false);
+        if (kde_session == 1) {
+          var shellObj = Components.classes["@mozilla.org/file/local;1"]
+            .createInstance(Components.interfaces.nsILocalFile);
+          shellObj.initWithPath("/usr/bin/kwriteconfig");
+          var process = Components.classes["@mozilla.org/process/util;1"]
+            .createInstance(Components.interfaces.nsIProcess);
+          process.init(shellObj);
+          var args = ["--file", "kdeglobals", "--group", "General", "--key",
+              "BrowserApplication", "waterfox-current"];
+          process.run(false, args, args.length);
+        }
       } catch (ex) {
         Cu.reportError(ex);
         return;
diff --git a/browser/components/shell/moz.build b/browser/components/shell/moz.build
index a1f9dac0aca2..5e2b6dba5586 100644
--- a/browser/components/shell/moz.build
+++ b/browser/components/shell/moz.build
@@ -33,6 +33,8 @@ elif 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
 
     SOURCES += [
         'nsGNOMEShellService.cpp',
+        'nsKDEShellService.cpp',
+        'nsUnixShellService.cpp',
     ]
 elif CONFIG['OS_ARCH'] == 'WINNT':
     SOURCES += [
diff --git a/browser/components/shell/nsKDEShellService.cpp b/browser/components/shell/nsKDEShellService.cpp
new file mode 100644
index 000000000000..d14f52c8a40f
--- /dev/null
+++ b/browser/components/shell/nsKDEShellService.cpp
@@ -0,0 +1,150 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/ArrayUtils.h"
+
+#include "nsCOMPtr.h"
+#include "nsKDEShellService.h"
+#include "nsShellService.h"
+#include "nsKDEUtils.h"
+#include "nsIPrefService.h"
+#include "nsIProcess.h"
+#include "nsIFile.h"
+#include "nsServiceManagerUtils.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIMutableArray.h"
+#include "nsISupportsPrimitives.h"
+#include "nsArrayUtils.h"
+
+using namespace mozilla;
+
+nsresult
+nsKDEShellService::Init()
+{
+    if( !nsKDEUtils::kdeSupport())
+        return NS_ERROR_NOT_AVAILABLE;
+    return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(nsKDEShellService, nsIGNOMEShellService, nsIShellService)
+
+NS_IMETHODIMP
+nsKDEShellService::IsDefaultBrowser(bool aForAllTypes,
+                                    bool* aIsDefaultBrowser)
+{
+    *aIsDefaultBrowser = false;
+
+    nsCOMPtr<nsIMutableArray> command = do_CreateInstance( NS_ARRAY_CONTRACTID );
+    if (!command)
+        return NS_ERROR_FAILURE;
+
+    nsCOMPtr<nsISupportsCString> str = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+    if (!str)
+        return NS_ERROR_FAILURE;
+
+    str->SetData( NS_LITERAL_CSTRING( "ISDEFAULTBROWSER" ));
+    command->AppendElement( str );
+
+    if( nsKDEUtils::command( command ))
+        *aIsDefaultBrowser = true;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsKDEShellService::SetDefaultBrowser(bool aClaimAllTypes,
+                                     bool aForAllUsers)
+{
+    nsCOMPtr<nsIMutableArray> command = do_CreateInstance( NS_ARRAY_CONTRACTID );
+    if (!command)
+        return NS_ERROR_FAILURE;
+
+    nsCOMPtr<nsISupportsCString> cmdstr = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+    nsCOMPtr<nsISupportsCString> paramstr = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+    if (!cmdstr || !paramstr)
+        return NS_ERROR_FAILURE;
+
+    cmdstr->SetData( NS_LITERAL_CSTRING( "SETDEFAULTBROWSER" ));
+    command->AppendElement( cmdstr );
+
+    paramstr->SetData( aClaimAllTypes ? NS_LITERAL_CSTRING( "ALLTYPES" ) : NS_LITERAL_CSTRING( "NORMAL" ));
+    command->AppendElement( paramstr );
+
+    return nsKDEUtils::command( command ) ? NS_OK : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsKDEShellService::GetCanSetDesktopBackground(bool* aResult)
+{
+  *aResult = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsKDEShellService::SetDesktopBackground(dom::Element* aElement,
+                                        int32_t aPosition,
+                                        const nsACString& aImageName)
+{
+    return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsKDEShellService::GetDesktopBackgroundColor(PRUint32 *aColor)
+{
+    return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsKDEShellService::SetDesktopBackgroundColor(PRUint32 aColor)
+{
+    return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsKDEShellService::OpenApplication(PRInt32 aApplication)
+{
+    nsCOMPtr<nsIMutableArray> command = do_CreateInstance( NS_ARRAY_CONTRACTID );
+    if (!command)
+        return NS_ERROR_FAILURE;
+
+    nsCOMPtr<nsISupportsCString> str = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+    if (!str)
+        return NS_ERROR_FAILURE;
+
+    if( aApplication == APPLICATION_MAIL )
+        str->SetData( NS_LITERAL_CSTRING( "OPENMAIL" ));
+    else if( aApplication == APPLICATION_NEWS )
+        str->SetData( NS_LITERAL_CSTRING( "OPENNEWS" ));
+    else
+        return NS_ERROR_NOT_IMPLEMENTED;
+
+    command->AppendElement( str );
+    return nsKDEUtils::command( command ) ? NS_OK : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsKDEShellService::OpenApplicationWithURI(nsIFile* aApplication, const nsACString& aURI)
+{
+    nsCOMPtr<nsIMutableArray> command = do_CreateInstance( NS_ARRAY_CONTRACTID );
+    if (!command)
+        return NS_ERROR_FAILURE;
+
+    nsCOMPtr<nsISupportsCString> cmdstr = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+    nsCOMPtr<nsISupportsCString> appstr = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+    nsCOMPtr<nsISupportsCString> uristr = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+    if (!cmdstr || !appstr || !uristr)
+        return NS_ERROR_FAILURE;
+
+    cmdstr->SetData( NS_LITERAL_CSTRING( "RUN" ));
+    command->AppendElement( cmdstr );
+    nsAutoCString app;
+    nsresult rv = aApplication->GetNativePath( app );
+    NS_ENSURE_SUCCESS( rv, rv );
+    appstr->SetData( app );
+    command->AppendElement( appstr );
+    uristr->SetData( aURI );
+    command->AppendElement( uristr );
+    return nsKDEUtils::command( command ) ? NS_OK : NS_ERROR_FAILURE;
+}
+
diff --git a/browser/components/shell/nsKDEShellService.h b/browser/components/shell/nsKDEShellService.h
new file mode 100644
index 000000000000..8b0bb1916435
--- /dev/null
+++ b/browser/components/shell/nsKDEShellService.h
@@ -0,0 +1,32 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nskdeshellservice_h____
+#define nskdeshellservice_h____
+
+#include "nsIGNOMEShellService.h"
+#include "nsToolkitShellService.h"
+#include "nsString.h"
+#include "mozilla/Attributes.h"
+
+class nsKDEShellService final : public nsIGNOMEShellService,
+                                public nsToolkitShellService
+{
+public:
+  nsKDEShellService() : mCheckedThisSession(false) { }
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISHELLSERVICE
+  NS_DECL_NSIGNOMESHELLSERVICE
+
+  nsresult Init();
+
+private:
+  ~nsKDEShellService() {}
+
+  bool mCheckedThisSession;
+};
+
+#endif // nskdeshellservice_h____
diff --git a/browser/components/shell/nsUnixShellService.cpp b/browser/components/shell/nsUnixShellService.cpp
new file mode 100644
index 000000000000..a6827209d9e7
--- /dev/null
+++ b/browser/components/shell/nsUnixShellService.cpp
@@ -0,0 +1,22 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+
+#include "nsUnixShellService.h"
+#include "nsGNOMEShellService.h"
+#include "nsKDEShellService.h"
+#include "nsKDEUtils.h"
+#include "mozilla/ModuleUtils.h"
+
+NS_GENERIC_FACTORY_CONSTRUCTOR_INIT(nsGNOMEShellService, Init)
+NS_GENERIC_FACTORY_CONSTRUCTOR_INIT(nsKDEShellService, Init)
+
+NS_IMETHODIMP
+nsUnixShellServiceConstructor(nsISupports *aOuter, REFNSIID aIID, void **aResult)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDEShellServiceConstructor( aOuter, aIID, aResult );
+    return nsGNOMEShellServiceConstructor( aOuter, aIID, aResult );
+}
diff --git a/browser/components/shell/nsUnixShellService.h b/browser/components/shell/nsUnixShellService.h
new file mode 100644
index 000000000000..26b5dbac47dd
--- /dev/null
+++ b/browser/components/shell/nsUnixShellService.h
@@ -0,0 +1,15 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+
+#ifndef nsunixshellservice_h____
+#define nsunixshellservice_h____
+
+#include "nsIGNOMEShellService.h"
+
+NS_IMETHODIMP
+nsUnixShellServiceConstructor(nsISupports *aOuter, REFNSIID aIID, void **aResult);
+
+#endif // nsunixshellservice_h____
diff --git a/modules/libpref/Preferences.cpp b/modules/libpref/Preferences.cpp
index a7c537abab20..33fa2a2f1444 100644
--- a/modules/libpref/Preferences.cpp
+++ b/modules/libpref/Preferences.cpp
@@ -86,6 +86,7 @@
 #include "PLDHashTable.h"
 #include "plstr.h"
 #include "prlink.h"
+#include "nsKDEUtils.h"
 
 #ifdef MOZ_MEMORY
 #  include "mozmemory.h"
@@ -4479,6 +4480,7 @@ static nsresult pref_ReadDefaultPrefs(const RefPtr<nsZipArchive> jarReader,
     "winpref.js"
 #elif defined(XP_UNIX)
     "unix.js"
+    , "" // placeholder for KDE  (empty is otherwise harmless)
 #  if defined(_AIX)
     ,
     "aix.js"
@@ -4488,6 +4490,17 @@ static nsresult pref_ReadDefaultPrefs(const RefPtr<nsZipArchive> jarReader,
 #endif
   };
 
+  if(nsKDEUtils::kdeSession()) { // TODO what if some setup actually requires the helper?
+    for(int i = 0;
+        i < MOZ_ARRAY_LENGTH(specialFiles);
+        ++i ) {
+      if( *specialFiles[ i ] == '\0' ) {
+        specialFiles[ i ] = "kde.js";
+        break;
+      }
+    }
+  }
+
   rv = pref_LoadPrefsInDir(defaultPrefDir, specialFiles,
                            ArrayLength(specialFiles));
   if (NS_FAILED(rv)) {
@@ -4545,7 +4558,7 @@ static nsresult pref_ReadDefaultPrefs(const RefPtr<nsZipArchive> jarReader,
       }
 
       // Do we care if a file provided by this process fails to load?
-      pref_LoadPrefsInDir(path, nullptr, 0);
+      pref_LoadPrefsInDir(path, specialFiles, ArrayLength(specialFiles));
     }
   }
 
diff --git a/modules/libpref/moz.build b/modules/libpref/moz.build
index 25f7d9869d10..ca72042dc697 100644
--- a/modules/libpref/moz.build
+++ b/modules/libpref/moz.build
@@ -36,6 +36,10 @@ UNIFIED_SOURCES += [
     'SharedPrefMap.cpp',
 ]
 
+LOCAL_INCLUDES += [
+    '/toolkit/xre'
+]
+
 XPCOM_MANIFESTS += [
     'components.conf',
 ]
diff --git a/python/mozbuild/mozpack/chrome/flags.py b/python/mozbuild/mozpack/chrome/flags.py
index 92e9ff4eca9f..78c86ac9f426 100644
--- a/python/mozbuild/mozpack/chrome/flags.py
+++ b/python/mozbuild/mozpack/chrome/flags.py
@@ -228,6 +228,7 @@ class Flags(OrderedDict):
         'xpcnativewrappers': Flag,
         'tablet': Flag,
         'process': StringFlag,
+        'desktop': StringFlag,
     }
     RE = re.compile(r'([!<>=]+)')
 
diff --git a/python/mozbuild/mozpack/chrome/manifest.py b/python/mozbuild/mozpack/chrome/manifest.py
index 1c857bf5e79e..e54d3b5aaba9 100644
--- a/python/mozbuild/mozpack/chrome/manifest.py
+++ b/python/mozbuild/mozpack/chrome/manifest.py
@@ -44,6 +44,7 @@ class ManifestEntry(object):
         'tablet',
         'process',
         'contentaccessible',
+	'desktop',
     ]
 
     def __init__(self, base, *flags):
diff --git a/toolkit/components/downloads/moz.build b/toolkit/components/downloads/moz.build
index 493c1a442ece..720942aacdea 100644
--- a/toolkit/components/downloads/moz.build
+++ b/toolkit/components/downloads/moz.build
@@ -46,5 +46,9 @@ if CONFIG['MOZ_PLACES']:
 
 FINAL_LIBRARY = 'xul'
 
+LOCAL_INCLUDES += [
+    '/toolkit/xre'
+]
+
 with Files('**'):
     BUG_COMPONENT = ('Toolkit', 'Downloads API')
diff --git a/toolkit/content/jar.mn b/toolkit/content/jar.mn
index ed63fa26960b..28fa25143ff9 100644
--- a/toolkit/content/jar.mn
+++ b/toolkit/content/jar.mn
@@ -68,6 +68,8 @@ toolkit.jar:
    content/global/bindings/datepicker.js       (widgets/datepicker.js)
    content/global/bindings/datetimebox.css     (widgets/datetimebox.css)
 *  content/global/bindings/dialog.xml          (widgets/dialog.xml)
+*  content/global/bindings/dialog-kde.xml      (widgets/dialog-kde.xml)
+% override chrome://global/content/bindings/dialog.xml chrome://global/content/bindings/dialog-kde.xml desktop=kde
    content/global/bindings/general.xml         (widgets/general.xml)
    content/global/bindings/popup.xml           (widgets/popup.xml)
    content/global/bindings/richlistbox.xml     (widgets/richlistbox.xml)
diff --git a/toolkit/content/widgets/dialog-kde.xml b/toolkit/content/widgets/dialog-kde.xml
new file mode 100644
index 000000000000..2ea14e32901b
--- /dev/null
+++ b/toolkit/content/widgets/dialog-kde.xml
@@ -0,0 +1,499 @@
+<?xml version="1.0"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<!DOCTYPE bindings [
+  <!ENTITY % globalKeysDTD SYSTEM "chrome://global/locale/globalKeys.dtd">
+  %globalKeysDTD;
+]>
+
+<bindings id="dialogBindings"
+          xmlns="http://www.mozilla.org/xbl"
+          xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+          xmlns:xbl="http://www.mozilla.org/xbl">
+
+  <binding id="dialog">
+    <content>
+      <xul:vbox class="box-inherit dialog-content-box" flex="1">
+        <children/>
+      </xul:vbox>
+
+      <xul:hbox class="dialog-button-box" anonid="buttons"
+                xbl:inherits="pack=buttonpack,align=buttonalign,dir=buttondir,orient=buttonorient"
+#ifdef XP_UNIX_GNOME
+                >
+        <xul:button dlgtype="disclosure" class="dialog-button" hidden="true"/>
+        <xul:button dlgtype="help" class="dialog-button" hidden="true"/>
+        <xul:button dlgtype="extra2" class="dialog-button" hidden="true"/>
+        <xul:button dlgtype="extra1" class="dialog-button" hidden="true"/>
+        <xul:spacer anonid="spacer" flex="1"/>
+        <xul:button dlgtype="cancel" class="dialog-button"/>
+        <xul:button dlgtype="accept" class="dialog-button" xbl:inherits="disabled=buttondisabledaccept"/>
+#elif XP_UNIX
+                >
+        <xul:button dlgtype="help" class="dialog-button" hidden="true"/>
+        <xul:button dlgtype="extra2" class="dialog-button" hidden="true"/>
+        <xul:spacer anonid="spacer" flex="1"/>
+        <xul:button dlgtype="accept" class="dialog-button" xbl:inherits="disabled=buttondisabledaccept"/>
+        <xul:button dlgtype="extra1" class="dialog-button" hidden="true"/>
+        <xul:button dlgtype="cancel" class="dialog-button"/>
+        <xul:button dlgtype="disclosure" class="dialog-button" hidden="true"/>
+#else
+                pack="end">
+        <xul:button dlgtype="extra2" class="dialog-button" hidden="true"/>
+        <xul:spacer anonid="spacer" flex="1" hidden="true"/>
+        <xul:button dlgtype="accept" class="dialog-button" xbl:inherits="disabled=buttondisabledaccept"/>
+        <xul:button dlgtype="extra1" class="dialog-button" hidden="true"/>
+        <xul:button dlgtype="cancel" class="dialog-button"/>
+        <xul:button dlgtype="help" class="dialog-button" hidden="true"/>
+        <xul:button dlgtype="disclosure" class="dialog-button" hidden="true"/>
+#endif
+      </xul:hbox>
+
+    <xul:keyset>
+      <xul:key phase="capturing" oncommand="document.documentElement.openHelp(event)"
+#ifdef XP_MACOSX
+           key="&openHelpMac.commandkey;" modifiers="accel"/>
+#else
+           keycode="&openHelp.commandkey;"/>
+#endif
+    </xul:keyset>
+
+    </content>
+
+    <implementation>
+      <field name="_mStrBundle">null</field>
+      <field name="_closeHandler">(function(event) {
+        if (!document.documentElement.cancelDialog())
+          event.preventDefault();
+      })</field>
+
+      <!-- Gets populated by elements that are passed to document.l10n.setAttributes
+           to localize the dialog buttons. Needed to properly size the dialog after
+           the asynchronous translation. -->
+      <field name="_l10nButtons">[]</field>
+
+      <property name="buttons"
+                onget="return this.getAttribute('buttons');"
+                onset="this._configureButtons(val); return val;"/>
+
+      <property name="defaultButton">
+        <getter>
+        <![CDATA[
+          if (this.hasAttribute("defaultButton"))
+            return this.getAttribute("defaultButton");
+          return "accept"; // default to the accept button
+        ]]>
+        </getter>
+        <setter>
+        <![CDATA[
+          this._setDefaultButton(val);
+          return val;
+        ]]>
+        </setter>
+      </property>
+
+      <method name="acceptDialog">
+        <body>
+        <![CDATA[
+          return this._doButtonCommand("accept");
+        ]]>
+        </body>
+      </method>
+
+      <method name="cancelDialog">
+        <body>
+        <![CDATA[
+          return this._doButtonCommand("cancel");
+        ]]>
+        </body>
+      </method>
+
+      <method name="getButton">
+        <parameter name="aDlgType"/>
+        <body>
+        <![CDATA[
+          return this._buttons[aDlgType];
+        ]]>
+        </body>
+      </method>
+
+      <method name="moveToAlertPosition">
+        <body>
+        <![CDATA[
+          // hack. we need this so the window has something like its final size
+          if (window.outerWidth == 1) {
+            dump("Trying to position a sizeless window; caller should have called sizeToContent() or sizeTo(). See bug 75649.\n");
+            sizeToContent();
+          }
+
+          if (opener) {
+            var xOffset = (opener.outerWidth - window.outerWidth) / 2;
+            var yOffset = opener.outerHeight / 5;
+
+            var newX = opener.screenX + xOffset;
+            var newY = opener.screenY + yOffset;
+          } else {
+            newX = (screen.availWidth - window.outerWidth) / 2;
+            newY = (screen.availHeight - window.outerHeight) / 2;
+          }
+
+          // ensure the window is fully onscreen (if smaller than the screen)
+          if (newX < screen.availLeft)
+            newX = screen.availLeft + 20;
+          if ((newX + window.outerWidth) > (screen.availLeft + screen.availWidth))
+            newX = (screen.availLeft + screen.availWidth) - window.outerWidth - 20;
+
+          if (newY < screen.availTop)
+            newY = screen.availTop + 20;
+          if ((newY + window.outerHeight) > (screen.availTop + screen.availHeight))
+            newY = (screen.availTop + screen.availHeight) - window.outerHeight - 60;
+
+          window.moveTo( newX, newY );
+        ]]>
+        </body>
+      </method>
+
+      <method name="centerWindowOnScreen">
+        <body>
+        <![CDATA[
+          var xOffset = screen.availWidth / 2 - window.outerWidth / 2;
+          var yOffset = screen.availHeight / 2 - window.outerHeight / 2;
+
+          xOffset = xOffset > 0 ? xOffset : 0;
+          yOffset = yOffset > 0 ? yOffset : 0;
+          window.moveTo(xOffset, yOffset);
+        ]]>
+        </body>
+      </method>
+
+      <constructor>
+      <![CDATA[
+        this._configureButtons(this.buttons);
+
+        // listen for when window is closed via native close buttons
+        window.addEventListener("close", this);
+
+        // for things that we need to initialize after onload fires
+        window.addEventListener("load", this);
+
+        window.moveToAlertPosition = this.moveToAlertPosition;
+        window.centerWindowOnScreen = this.centerWindowOnScreen;
+      ]]>
+      </constructor>
+
+      <method name="handleEvent">
+        <parameter name="aEvent"/>
+        <body><![CDATA[
+          switch (aEvent.type) {
+            case "close": {
+              this._closeHandler(aEvent);
+              break;
+            }
+            case "load": {
+              this.postLoadInit(aEvent);
+              break;
+            }
+          }
+        ]]></body>
+      </method>
+
+      <method name="postLoadInit">
+        <parameter name="aEvent"/>
+        <body>
+        <![CDATA[
+          function focusInit() {
+            const dialog = document.documentElement;
+            const defaultButton = dialog.getButton(dialog.defaultButton);
+            // give focus to the first focusable element in the dialog
+            if (!document.commandDispatcher.focusedElement) {
+              document.commandDispatcher.advanceFocusIntoSubtree(dialog);
+
+              var focusedElt = document.commandDispatcher.focusedElement;
+              if (focusedElt) {
+                var initialFocusedElt = focusedElt;
+                while (focusedElt.localName == "tab" ||
+                       focusedElt.getAttribute("noinitialfocus") == "true") {
+                  document.commandDispatcher.advanceFocusIntoSubtree(focusedElt);
+                  focusedElt = document.commandDispatcher.focusedElement;
+                  if (focusedElt == initialFocusedElt) {
+                    if (focusedElt.getAttribute("noinitialfocus") == "true") {
+                      focusedElt.blur();
+                    }
+                    break;
+                  }
+                }
+
+                if (initialFocusedElt.localName == "tab") {
+                  if (focusedElt.hasAttribute("dlgtype")) {
+                    // We don't want to focus on anonymous OK, Cancel, etc. buttons,
+                    // so return focus to the tab itself
+                    initialFocusedElt.focus();
+                  }
+                } else if (!/Mac/.test(navigator.platform) &&
+                           focusedElt.hasAttribute("dlgtype") && focusedElt != defaultButton) {
+                  defaultButton.focus();
+                }
+              }
+            }
+
+            try {
+              if (defaultButton)
+                window.notifyDefaultButtonLoaded(defaultButton);
+            } catch (e) { }
+          }
+
+          // Give focus after onload completes, see bug 103197.
+          setTimeout(focusInit, 0);
+
+          if (this._l10nButtons.length) {
+            document.l10n.translateElements(this._l10nButtons).then(() => {
+              window.sizeToContent();
+            });
+          }
+        ]]>
+        </body>
+      </method>
+
+      <method name="openHelp">
+        <parameter name="event"/>
+        <body>
+        <![CDATA[
+          var helpButton = document.documentElement.getButton("help");
+          if (helpButton.disabled || helpButton.hidden)
+            return;
+          this._fireButtonEvent("help");
+          event.stopPropagation();
+          event.preventDefault();
+        ]]>
+        </body>
+      </method>
+
+      <property name="mStrBundle">
+        <getter>
+        <![CDATA[
+          if (!this._mStrBundle) {
+            // need to create string bundle manually instead of using <xul:stringbundle/>
+            // see bug 63370 for details
+            this._mStrBundle = Cc["@mozilla.org/intl/stringbundle;1"]
+                                 .getService(Ci.nsIStringBundleService)
+                                 .createBundle("chrome://global/locale/dialog.properties");
+          }
+          return this._mStrBundle;
+        ]]></getter>
+      </property>
+
+      <method name="_configureButtons">
+        <parameter name="aButtons"/>
+        <body>
+        <![CDATA[
+          // by default, get all the anonymous button elements
+          var buttons = {};
+          this._buttons = buttons;
+          buttons.accept = document.getAnonymousElementByAttribute(this, "dlgtype", "accept");
+          buttons.cancel = document.getAnonymousElementByAttribute(this, "dlgtype", "cancel");
+          buttons.extra1 = document.getAnonymousElementByAttribute(this, "dlgtype", "extra1");
+          buttons.extra2 = document.getAnonymousElementByAttribute(this, "dlgtype", "extra2");
+          buttons.help = document.getAnonymousElementByAttribute(this, "dlgtype", "help");
+          buttons.disclosure = document.getAnonymousElementByAttribute(this, "dlgtype", "disclosure");
+
+          for (let button in buttons) {
+            customElements.upgrade(buttons[button]);
+          }
+
+          // look for any overriding explicit button elements
+          var exBtns = this.getElementsByAttribute("dlgtype", "*");
+          var dlgtype;
+          var i;
+          for (i = 0; i < exBtns.length; ++i) {
+            dlgtype = exBtns[i].getAttribute("dlgtype");
+            buttons[dlgtype].hidden = true; // hide the anonymous button
+            buttons[dlgtype] = exBtns[i];
+          }
+
+          // add the label and oncommand handler to each button
+          for (dlgtype in buttons) {
+            var button = buttons[dlgtype];
+            button.addEventListener("command", this._handleButtonCommand, true);
+
+            // don't override custom labels with pre-defined labels on explicit buttons
+            if (!button.hasAttribute("label")) {
+              // dialog attributes override the default labels in dialog.properties
+              if (this.hasAttribute("buttonlabel" + dlgtype)) {
+                button.setAttribute("label", this.getAttribute("buttonlabel" + dlgtype));
+                if (this.hasAttribute("buttonaccesskey" + dlgtype))
+                  button.setAttribute("accesskey", this.getAttribute("buttonaccesskey" + dlgtype));
+              } else if (this.hasAttribute("buttonid" + dlgtype)) {
+                document.l10n.setAttributes(button, this.getAttribute("buttonid" + dlgtype));
+                this._l10nButtons.push(button);
+              } else if (dlgtype != "extra1" && dlgtype != "extra2") {
+                button.setAttribute("label", this.mStrBundle.GetStringFromName("button-" + dlgtype));
+                var accessKey = this.mStrBundle.GetStringFromName("accesskey-" + dlgtype);
+                if (accessKey)
+                  button.setAttribute("accesskey", accessKey);
+              }
+            }
+            // allow specifying alternate icons in the dialog header
+            if (!button.hasAttribute("icon")) {
+              // if there's an icon specified, use that
+              if (this.hasAttribute("buttonicon" + dlgtype))
+                button.setAttribute("icon", this.getAttribute("buttonicon" + dlgtype));
+              // otherwise set defaults
+              else
+                switch (dlgtype) {
+                  case "accept":
+                    button.setAttribute("icon", "accept");
+                    break;
+                  case "cancel":
+                    button.setAttribute("icon", "cancel");
+                    break;
+                  case "disclosure":
+                    button.setAttribute("icon", "properties");
+                    break;
+                  case "help":
+                    button.setAttribute("icon", "help");
+                    break;
+                  default:
+                    break;
+                }
+            }
+          }
+
+          // ensure that hitting enter triggers the default button command
+          this.defaultButton = this.defaultButton;
+
+          // if there is a special button configuration, use it
+          if (aButtons) {
+            // expect a comma delimited list of dlgtype values
+            var list = aButtons.split(",");
+
+            // mark shown dlgtypes as true
+            var shown = { accept: false, cancel: false, help: false,
+                          disclosure: false, extra1: false, extra2: false };
+            for (i = 0; i < list.length; ++i)
+              shown[list[i].replace(/ /g, "")] = true;
+
+            // hide/show the buttons we want
+            for (dlgtype in buttons)
+              buttons[dlgtype].hidden = !shown[dlgtype];
+
+            // show the spacer on Windows only when the extra2 button is present
+            if (/Win/.test(navigator.platform)) {
+              var spacer = document.getAnonymousElementByAttribute(this, "anonid", "spacer");
+              spacer.removeAttribute("hidden");
+              spacer.setAttribute("flex", shown.extra2 ? "1" : "0");
+            }
+          }
+        ]]>
+        </body>
+      </method>
+
+      <method name="_setDefaultButton">
+        <parameter name="aNewDefault"/>
+        <body>
+        <![CDATA[
+          // remove the default attribute from the previous default button, if any
+          var oldDefaultButton = this.getButton(this.defaultButton);
+          if (oldDefaultButton)
+            oldDefaultButton.removeAttribute("default");
+
+          var newDefaultButton = this.getButton(aNewDefault);
+          if (newDefaultButton) {
+            this.setAttribute("defaultButton", aNewDefault);
+            newDefaultButton.setAttribute("default", "true");
+          } else {
+            this.setAttribute("defaultButton", "none");
+            if (aNewDefault != "none")
+              dump("invalid new default button: " + aNewDefault + ", assuming: none\n");
+          }
+        ]]>
+        </body>
+      </method>
+
+      <method name="_handleButtonCommand">
+        <parameter name="aEvent"/>
+        <body>
+        <![CDATA[
+          return document.documentElement._doButtonCommand(
+                                        aEvent.target.getAttribute("dlgtype"));
+        ]]>
+        </body>
+      </method>
+
+      <method name="_doButtonCommand">
+        <parameter name="aDlgType"/>
+        <body>
+        <![CDATA[
+          var button = this.getButton(aDlgType);
+          if (!button.disabled) {
+            var noCancel = this._fireButtonEvent(aDlgType);
+            if (noCancel) {
+              if (aDlgType == "accept" || aDlgType == "cancel") {
+                var closingEvent = new CustomEvent("dialogclosing", {
+                  bubbles: true,
+                  detail: { button: aDlgType },
+                });
+                this.dispatchEvent(closingEvent);
+                window.close();
+              }
+            }
+            return noCancel;
+          }
+          return true;
+        ]]>
+        </body>
+      </method>
+
+      <method name="_fireButtonEvent">
+        <parameter name="aDlgType"/>
+        <body>
+        <![CDATA[
+          var event = document.createEvent("Events");
+          event.initEvent("dialog" + aDlgType, true, true);
+
+          // handle dom event handlers
+          return this.dispatchEvent(event);
+        ]]>
+        </body>
+      </method>
+
+      <method name="_hitEnter">
+        <parameter name="evt"/>
+        <body>
+        <![CDATA[
+          if (evt.defaultPrevented)
+            return;
+
+          var btn = this.getButton(this.defaultButton);
+          if (btn)
+            this._doButtonCommand(this.defaultButton);
+        ]]>
+        </body>
+      </method>
+
+    </implementation>
+
+    <handlers>
+      <handler event="keypress" keycode="VK_RETURN"
+               group="system" action="this._hitEnter(event);"/>
+      <handler event="keypress" keycode="VK_ESCAPE" group="system">
+        if (!event.defaultPrevented)
+          this.cancelDialog();
+      </handler>
+#ifdef XP_MACOSX
+      <handler event="keypress" key="." modifiers="meta" phase="capturing" action="this.cancelDialog();"/>
+#else
+      <handler event="focus" phase="capturing">
+        var btn = this.getButton(this.defaultButton);
+        if (btn)
+          btn.setAttribute("default", event.originalTarget == btn ||
+                           !(event.originalTarget.localName == "button" ||
+                             event.originalTarget.localName == "toolbarbutton"));
+      </handler>
+#endif
+    </handlers>
+
+  </binding>
+
+</bindings>
diff --git a/toolkit/mozapps/downloads/HelperAppDlg.jsm b/toolkit/mozapps/downloads/HelperAppDlg.jsm
index 6b385170200d..880c160e5ea3 100644
--- a/toolkit/mozapps/downloads/HelperAppDlg.jsm
+++ b/toolkit/mozapps/downloads/HelperAppDlg.jsm
@@ -1209,26 +1209,56 @@ nsUnknownContentTypeDialog.prototype = {
         this.chosenApp = params.handlerApp;
       }
     } else if ("@mozilla.org/applicationchooser;1" in Cc) {
-      var nsIApplicationChooser = Ci.nsIApplicationChooser;
-      var appChooser = Cc["@mozilla.org/applicationchooser;1"].createInstance(
-        nsIApplicationChooser
-      );
-      appChooser.init(
-        this.mDialog,
-        this.dialogElement("strings").getString("chooseAppFilePickerTitle")
-      );
-      var contentTypeDialogObj = this;
-      let appChooserCallback = function appChooserCallback_done(aResult) {
-        if (aResult) {
-          contentTypeDialogObj.chosenApp = aResult.QueryInterface(
-            Ci.nsILocalHandlerApp
-          );
-        }
-        contentTypeDialogObj.finishChooseApp();
-      };
-      appChooser.open(this.mLauncher.MIMEInfo.MIMEType, appChooserCallback);
-      // The finishChooseApp is called from appChooserCallback
-      return;
+      // handle the KDE case which is implemented in the filepicker
+      // therefore falling back to Gtk2 like behaviour if KDE is running
+      // FIXME this should be better handled in the nsIApplicationChooser
+      // interface
+      var env = Components.classes["@mozilla.org/process/environment;1"]
+                          .getService(Components.interfaces.nsIEnvironment);
+      if (env.get('KDE_FULL_SESSION') == "true")
+      {
+        var nsIFilePicker = Ci.nsIFilePicker;
+        var fp = Cc["@mozilla.org/filepicker;1"]
+                    .createInstance(nsIFilePicker);
+        fp.init(this.mDialog,
+                this.dialogElement("strings").getString("chooseAppFilePickerTitle"),
+                nsIFilePicker.modeOpen);
+
+        fp.appendFilters(nsIFilePicker.filterApps);
+
+        fp.open(aResult => {
+          if (aResult == nsIFilePicker.returnOK && fp.file) {
+            // Remember the file they chose to run.
+            var localHandlerApp =
+              Cc["@mozilla.org/uriloader/local-handler-app;1"].
+                         createInstance(Ci.nsILocalHandlerApp);
+            localHandlerApp.executable = fp.file;
+            this.chosenApp = localHandlerApp;
+          }
+          this.finishChooseApp();
+        });
+      } else {
+        var nsIApplicationChooser = Ci.nsIApplicationChooser;
+        var appChooser = Cc["@mozilla.org/applicationchooser;1"].createInstance(
+          nsIApplicationChooser
+        );
+        appChooser.init(
+          this.mDialog,
+          this.dialogElement("strings").getString("chooseAppFilePickerTitle")
+        );
+        var contentTypeDialogObj = this;
+        let appChooserCallback = function appChooserCallback_done(aResult) {
+          if (aResult) {
+            contentTypeDialogObj.chosenApp = aResult.QueryInterface(
+              Ci.nsILocalHandlerApp
+            );
+          }
+          contentTypeDialogObj.finishChooseApp();
+        };
+        appChooser.open(this.mLauncher.MIMEInfo.MIMEType, appChooserCallback);
+        // The finishChooseApp is called from appChooserCallback
+        return;
+      }
     } else {
       var nsIFilePicker = Ci.nsIFilePicker;
       var fp = Cc["@mozilla.org/filepicker;1"].createInstance(nsIFilePicker);
diff --git a/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp b/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
index f099193e630d..8395044ae8db 100644
--- a/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
+++ b/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
@@ -19,6 +19,7 @@
 #include "nsInterfaceHashtable.h"
 #include "mozilla/Attributes.h"
 #include "nsIURI.h"
+#include "nsKDEUtils.h"
 
 using namespace mozilla;
 
@@ -42,6 +43,8 @@ class nsUnixSystemProxySettings final : public nsISystemProxySettings {
                                  nsACString& aResult);
   nsresult SetProxyResultFromGSettings(const char* aKeyBase, const char* aType,
                                        nsACString& aResult);
+  nsresult GetProxyFromKDE(const nsACString& aScheme, const nsACString& aHost,
+                           PRInt32 aPort, nsACString& aResult);
 };
 
 NS_IMPL_ISUPPORTS(nsUnixSystemProxySettings, nsISystemProxySettings)
@@ -384,6 +387,9 @@ nsresult nsUnixSystemProxySettings::GetProxyForURI(const nsACString& aSpec,
                                                    const nsACString& aHost,
                                                    const int32_t aPort,
                                                    nsACString& aResult) {
+  if (nsKDEUtils::kdeSupport())
+    return GetProxyFromKDE(aScheme, aHost, aPort, aResult);
+
   if (mProxySettings) {
     nsresult rv = GetProxyFromGSettings(aScheme, aHost, aPort, aResult);
     if (NS_SUCCEEDED(rv)) return rv;
@@ -392,6 +398,32 @@ nsresult nsUnixSystemProxySettings::GetProxyForURI(const nsACString& aSpec,
   return GetProxyFromEnvironment(aScheme, aHost, aPort, aResult);
 }
 
+nsresult
+nsUnixSystemProxySettings::GetProxyFromKDE(const nsACString& aScheme,
+                                           const nsACString& aHost,
+                                           PRInt32 aPort,
+                                           nsACString& aResult)
+{
+  nsAutoCString url;
+  url = aScheme;
+  url += "://";
+  url += aHost;
+  if( aPort >= 0 )
+  {
+    url += ":";
+    url += nsPrintfCString("%d", aPort);
+  }
+  nsTArray<nsCString> command;
+  command.AppendElement( NS_LITERAL_CSTRING( "GETPROXY" ));
+  command.AppendElement( url );
+  nsTArray<nsCString> result;
+  if( !nsKDEUtils::command( command, &result ) || result.Length() != 1 )
+    return NS_ERROR_FAILURE;
+  aResult = result[0];
+  return NS_OK;
+}
+
+
 NS_IMPL_COMPONENT_FACTORY(nsUnixSystemProxySettings) {
   auto result = MakeRefPtr<nsUnixSystemProxySettings>();
   result->Init();
diff --git a/toolkit/xre/moz.build b/toolkit/xre/moz.build
index 06604d5672cb..f2786d1b9788 100644
--- a/toolkit/xre/moz.build
+++ b/toolkit/xre/moz.build
@@ -89,7 +89,9 @@ elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'uikit':
         'UIKitDirProvider.mm',
     ]
 elif 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
+    EXPORTS += ['nsKDEUtils.h']
     UNIFIED_SOURCES += [
+        'nsKDEUtils.cpp',
         'nsNativeAppSupportUnix.cpp',
     ]
 else:
diff --git a/toolkit/xre/nsKDEUtils.cpp b/toolkit/xre/nsKDEUtils.cpp
new file mode 100644
index 000000000000..8035a2cc7850
--- /dev/null
+++ b/toolkit/xre/nsKDEUtils.cpp
@@ -0,0 +1,344 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsKDEUtils.h"
+#include "nsIWidget.h"
+#include "nsISupportsPrimitives.h"
+#include "nsIMutableArray.h"
+#include "nsComponentManagerUtils.h"
+#include "nsArrayUtils.h"
+
+#include <gtk/gtk.h>
+
+#include <limits.h>
+#include <stdio.h>
+#include <sys/wait.h>
+#include <sys/resource.h>
+#include <unistd.h>
+#include <X11/Xlib.h>
+// copied from X11/X.h as a hack since for an unknown
+// reason it's not picked up from X11/X.h
+#ifndef None
+#define None                 0L /* universal null resource or null atom */
+#endif
+
+//#define DEBUG_KDE
+#ifdef DEBUG_KDE
+#define KWATERFOXHELPER "kwaterfoxhelper"
+#else
+// not need for lib64, it's a binary
+#define KWATERFOXHELPER "/usr/lib/waterfox/kwaterfoxhelper"
+#endif
+
+#define KWATERFOXHELPER_VERSION 6
+#define MAKE_STR2( n ) #n
+#define MAKE_STR( n ) MAKE_STR2( n )
+
+static bool getKdeSession()
+    {
+    Display* dpy = XOpenDisplay( NULL );
+    if( dpy == NULL )
+        return false;
+    Atom kde_full_session = XInternAtom( dpy, "KDE_FULL_SESSION", true );
+    bool kde = false;
+    if( kde_full_session != None )
+        {
+        int cnt;
+        if( Atom* props = XListProperties( dpy, DefaultRootWindow( dpy ), &cnt ))
+            {
+            for( int i = 0;
+                 i < cnt;
+                 ++i )
+                {
+                if( props[ i ] == kde_full_session )
+                    {
+                    kde = true;
+#ifdef DEBUG_KDE
+                    fprintf( stderr, "KDE SESSION %d\n", kde );
+#endif
+                    break;
+                    }
+                }
+            XFree( props );
+            }
+        }
+    XCloseDisplay( dpy );
+    return kde;
+    }
+
+static bool getKdeSupport()
+    {
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING( "CHECK" ));
+    command.AppendElement( NS_LITERAL_CSTRING( MAKE_STR( KWATERFOXHELPER_VERSION )));
+    bool kde = nsKDEUtils::command( command );
+#ifdef DEBUG_KDE
+    fprintf( stderr, "KDE RUNNING %d\n", kde );
+#endif
+    return kde;
+    }
+
+nsKDEUtils::nsKDEUtils()
+    : commandFile( NULL )
+    , replyFile( NULL )
+    {
+    }
+
+nsKDEUtils::~nsKDEUtils()
+    {
+//    closeHelper(); not actually useful, exiting will close the fd too
+    }
+
+nsKDEUtils* nsKDEUtils::self()
+    {
+    static nsKDEUtils s;
+    return &s;
+    }
+
+static bool helperRunning = false;
+static bool helperFailed = false;
+
+bool nsKDEUtils::kdeSession()
+    {
+    static bool session = getKdeSession();
+    return session;
+    }
+
+bool nsKDEUtils::kdeSupport()
+    {
+    static bool support = kdeSession() && getKdeSupport();
+    return support && helperRunning;
+    }
+
+struct nsKDECommandData
+    {
+    FILE* file;
+    nsTArray<nsCString>* output;
+    GMainLoop* loop;
+    bool success;
+    };
+
+static gboolean kdeReadFunc( GIOChannel*, GIOCondition, gpointer data )
+    {
+    nsKDECommandData* p = static_cast< nsKDECommandData* >( data );
+    char buf[ 8192 ]; // TODO big enough
+    bool command_done = false;
+    bool command_failed = false;
+    while( !command_done && !command_failed && fgets( buf, 8192, p->file ) != NULL )
+        { // TODO what if the kernel splits a line into two chunks?
+//#ifdef DEBUG_KDE
+//        fprintf( stderr, "READ: %s %d\n", buf, feof( p->file ));
+//#endif
+        if( char* eol = strchr( buf, '\n' ))
+            *eol = '\0';
+        command_done = ( strcmp( buf, "\\1" ) == 0 );
+        command_failed = ( strcmp( buf, "\\0" ) == 0 );
+        nsAutoCString line( buf );
+        line.ReplaceSubstring( "\\n", "\n" );
+        line.ReplaceSubstring( "\\" "\\", "\\" ); //  \\ -> \ , i.e. unescape
+        if( p->output && !( command_done || command_failed ))
+            p->output->AppendElement( nsCString( buf )); // TODO utf8?
+        }
+    bool quit = false;
+    if( feof( p->file ) || command_failed )
+        {
+        quit = true;
+        p->success = false;
+        }
+    if( command_done )
+        { // reading one reply finished
+        quit = true;
+        p->success = true;
+        }
+    if( quit )
+        {
+        if( p->loop )
+            g_main_loop_quit( p->loop );
+        return FALSE;
+        }
+    return TRUE;
+    }
+
+bool nsKDEUtils::command( const nsTArray<nsCString>& command, nsTArray<nsCString>* output )
+    {
+    return self()->internalCommand( command, NULL, false, output );
+    }
+
+bool nsKDEUtils::command( nsIArray* command, nsIArray** output)
+    {
+    nsTArray<nsCString> in;
+    PRUint32 length;
+    command->GetLength( &length );
+    for ( PRUint32 i = 0; i < length; i++ )
+        {
+        nsCOMPtr<nsISupportsCString> str = do_QueryElementAt( command, i );
+        if( str )
+            {
+            nsAutoCString s;
+            str->GetData( s );
+            in.AppendElement( s );
+            }
+        }
+
+    nsTArray<nsCString> out;
+    bool ret = self()->internalCommand( in, NULL, false, &out );
+
+    if ( !output ) return ret;
+
+    nsCOMPtr<nsIMutableArray> result = do_CreateInstance( NS_ARRAY_CONTRACTID );
+    if ( !result ) return false;
+
+    for ( PRUint32 i = 0; i < out.Length(); i++ )
+        {
+        nsCOMPtr<nsISupportsCString> rstr = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+        if ( !rstr ) return false;
+
+        rstr->SetData( out[i] );
+        result->AppendElement( rstr );
+        }
+
+    NS_ADDREF( *output = result);
+    return ret;
+    }
+
+
+bool nsKDEUtils::commandBlockUi( const nsTArray<nsCString>& command, GtkWindow* parent, nsTArray<nsCString>* output )
+    {
+    return self()->internalCommand( command, parent, true, output );
+    }
+
+bool nsKDEUtils::internalCommand( const nsTArray<nsCString>& command, GtkWindow* parent, bool blockUi,
+    nsTArray<nsCString>* output )
+    {
+    if( !startHelper())
+        return false;
+    feedCommand( command );
+    // do not store the data in 'this' but in extra structure, just in case there
+    // is reentrancy (can there be? the event loop is re-entered)
+    nsKDECommandData data;
+    data.file = replyFile;
+    data.output = output;
+    data.success = false;
+    if( blockUi )
+        {
+        data.loop = g_main_loop_new( NULL, FALSE );
+        GtkWidget* window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
+        if( parent && gtk_window_get_group(parent) )
+            gtk_window_group_add_window( gtk_window_get_group(parent), GTK_WINDOW( window ));
+        gtk_widget_realize( window );
+        gtk_widget_set_sensitive( window, TRUE );
+        gtk_grab_add( window );
+        GIOChannel* channel = g_io_channel_unix_new( fileno( data.file ));
+        g_io_add_watch( channel, static_cast< GIOCondition >( G_IO_IN | G_IO_ERR | G_IO_HUP ), kdeReadFunc, &data );
+        g_io_channel_unref( channel );
+        g_main_loop_run( data.loop );
+        g_main_loop_unref( data.loop );
+        gtk_grab_remove( window );
+        gtk_widget_destroy( window );
+        }
+    else
+        {
+        data.loop = NULL;
+        while( kdeReadFunc( NULL, static_cast< GIOCondition >( 0 ), &data ))
+            ;
+        }
+    return data.success;
+    }
+
+bool nsKDEUtils::startHelper()
+    {
+    if( helperRunning )
+        return true;
+    if( helperFailed )
+        return false;
+    helperFailed = true;
+    int fdcommand[ 2 ];
+    int fdreply[ 2 ];
+    if( pipe( fdcommand ) < 0 )
+        return false;
+    if( pipe( fdreply ) < 0 )
+        {
+        close( fdcommand[ 0 ] );
+        close( fdcommand[ 1 ] );
+        return false;
+        }
+    char* args[ 2 ] = { const_cast< char* >( KWATERFOXHELPER ), NULL };
+    switch( fork())
+        {
+        case -1:
+            {
+            close( fdcommand[ 0 ] );
+            close( fdcommand[ 1 ] );
+            close( fdreply[ 0 ] );
+            close( fdreply[ 1 ] );
+            return false;
+            }
+        case 0: // child
+            {
+            if( dup2( fdcommand[ 0 ], STDIN_FILENO ) < 0 )
+                _exit( 1 );
+            if( dup2( fdreply[ 1 ], STDOUT_FILENO ) < 0 )
+                _exit( 1 );
+            int maxfd = 1024; // close all other fds
+            struct rlimit rl;
+            if( getrlimit( RLIMIT_NOFILE, &rl ) == 0 )
+                maxfd = rl.rlim_max;
+            for( int i = 3;
+                 i < maxfd;
+                 ++i )
+                close( i );
+#ifdef DEBUG_KDE
+            execvp( KWATERFOXHELPER, args );
+#else
+            execv( KWATERFOXHELPER, args );
+#endif
+            _exit( 1 ); // failed
+            }
+        default: // parent
+            {
+            commandFile = fdopen( fdcommand[ 1 ], "w" );
+            replyFile = fdopen( fdreply[ 0 ], "r" );
+            close( fdcommand[ 0 ] );
+            close( fdreply[ 1 ] );
+            if( commandFile == NULL || replyFile == NULL )
+                {
+                closeHelper();
+                return false;
+                }
+            // ok, helper ready, getKdeRunning() will check if it works
+            }
+        }
+    helperFailed = false;
+    helperRunning = true;
+    return true;
+    }
+
+void nsKDEUtils::closeHelper()
+    {
+    if( commandFile != NULL )
+        fclose( commandFile ); // this will also make the helper quit
+    if( replyFile != NULL )
+        fclose( replyFile );
+    helperRunning = false;
+    }
+
+void nsKDEUtils::feedCommand( const nsTArray<nsCString>& command )
+    {
+    for( int i = 0;
+         i < command.Length();
+         ++i )
+        {
+        nsCString line = command[ i ];
+        line.ReplaceSubstring( "\\", "\\" "\\" ); // \ -> \\ , i.e. escape
+        line.ReplaceSubstring( "\n", "\\n" );
+#ifdef DEBUG_KDE
+        fprintf( stderr, "COMM: %s\n", line.get());
+#endif
+        fputs( line.get(), commandFile );
+        fputs( "\n", commandFile );
+        }
+    fputs( "\\E\n", commandFile ); // done as \E, so it cannot happen in normal data
+    fflush( commandFile );
+    }
diff --git a/toolkit/xre/nsKDEUtils.h b/toolkit/xre/nsKDEUtils.h
new file mode 100644
index 000000000000..8729aebcaa1c
--- /dev/null
+++ b/toolkit/xre/nsKDEUtils.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsKDEUtils_h__
+#define nsKDEUtils_h__
+
+#include "nsString.h"
+#include "nsTArray.h"
+#include <stdio.h>
+
+typedef struct _GtkWindow GtkWindow;
+
+class nsIArray;
+
+class NS_EXPORT nsKDEUtils
+    {
+    public:
+        /* Returns true if running inside a KDE session (regardless of whether there is KDE
+           support available for Waterfox). This should be used e.g. when determining
+           dialog button order but not for code that requires the KDE support. */
+        static bool kdeSession();
+        /* Returns true if running inside a KDE session and KDE support is available
+           for Waterfox. This should be used everywhere where the external helper is needed. */
+        static bool kdeSupport();
+        /* Executes the given helper command, returns true if helper returned success. */
+        static bool command( const nsTArray<nsCString>& command, nsTArray<nsCString>* output = NULL );
+        static bool command( nsIArray* command, nsIArray** output = NULL );
+        /* Like command(), but additionally blocks the parent widget like if there was
+           a modal dialog shown and enters the event loop (i.e. there are still paint updates,
+           this is for commands that take long). */
+        static bool commandBlockUi( const nsTArray<nsCString>& command, GtkWindow* parent, nsTArray<nsCString>* output = NULL );
+
+    private:
+        nsKDEUtils();
+        ~nsKDEUtils();
+        static nsKDEUtils* self();
+        bool startHelper();
+        void closeHelper();
+        void feedCommand( const nsTArray<nsCString>& command );
+        bool internalCommand( const nsTArray<nsCString>& command, GtkWindow* parent, bool isParent,
+            nsTArray<nsCString>* output );
+        FILE* commandFile;
+        FILE* replyFile;
+    };
+
+#endif // nsKDEUtils
diff --git a/uriloader/exthandler/HandlerServiceParent.cpp b/uriloader/exthandler/HandlerServiceParent.cpp
index b5c0e83d6847..f223726a8ff0 100644
--- a/uriloader/exthandler/HandlerServiceParent.cpp
+++ b/uriloader/exthandler/HandlerServiceParent.cpp
@@ -6,7 +6,7 @@
 #include "ContentHandlerService.h"
 #include "nsStringEnumerator.h"
 #ifdef MOZ_WIDGET_GTK
-#  include "unix/nsGNOMERegistry.h"
+#  include "unix/nsCommonRegistry.h"
 #endif
 
 using mozilla::dom::ContentHandlerService;
@@ -287,7 +287,7 @@ mozilla::ipc::IPCResult HandlerServiceParent::RecvExistsForProtocolOS(
   }
 #ifdef MOZ_WIDGET_GTK
   // Check the GNOME registry for a protocol handler
-  *aHandlerExists = nsGNOMERegistry::HandlerExists(aProtocolScheme.get());
+  *aHandlerExists = nsCommonRegistry::HandlerExists(aProtocolScheme.get());
 #else
   *aHandlerExists = false;
 #endif
@@ -316,7 +316,7 @@ mozilla::ipc::IPCResult HandlerServiceParent::RecvExistsForProtocol(
   }
   rv = protoSvc->ExternalProtocolHandlerExists(aProtocolScheme.get(),
                                                aHandlerExists);
-
+##
   if (NS_WARN_IF(NS_FAILED(rv))) {
     *aHandlerExists = false;
   }
diff --git a/uriloader/exthandler/moz.build b/uriloader/exthandler/moz.build
index ec0ef6ce045d..c64a4bd88553 100644
--- a/uriloader/exthandler/moz.build
+++ b/uriloader/exthandler/moz.build
@@ -88,7 +88,9 @@ else:
 
 if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
     UNIFIED_SOURCES += [
+        'unix/nsCommonRegistry.cpp',
         'unix/nsGNOMERegistry.cpp',
+        'unix/nsKDERegistry.cpp',
         'unix/nsMIMEInfoUnix.cpp',
     ]
 elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
@@ -138,6 +140,7 @@ LOCAL_INCLUDES += [
     '/dom/ipc',
     '/netwerk/base',
     '/netwerk/protocol/http',
+    '/toolkit/xre',
 ]
 
 if CONFIG['MOZ_ENABLE_DBUS']:
diff --git a/uriloader/exthandler/unix/nsCommonRegistry.cpp b/uriloader/exthandler/unix/nsCommonRegistry.cpp
new file mode 100644
index 000000000000..630ab6147db3
--- /dev/null
+++ b/uriloader/exthandler/unix/nsCommonRegistry.cpp
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsCommonRegistry.h"
+
+#include "nsGNOMERegistry.h"
+#include "nsKDERegistry.h"
+#include "nsString.h"
+#include "nsKDEUtils.h"
+
+/* static */ bool
+nsCommonRegistry::HandlerExists(const char *aProtocolScheme)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::HandlerExists( aProtocolScheme );
+    return nsGNOMERegistry::HandlerExists( aProtocolScheme );
+}
+
+/* static */ nsresult
+nsCommonRegistry::LoadURL(nsIURI *aURL)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::LoadURL( aURL );
+    return nsGNOMERegistry::LoadURL( aURL );
+}
+
+/* static */ void
+nsCommonRegistry::GetAppDescForScheme(const nsACString& aScheme,
+                                     nsAString& aDesc)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::GetAppDescForScheme( aScheme, aDesc );
+    return nsGNOMERegistry::GetAppDescForScheme( aScheme, aDesc );
+}
+
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsCommonRegistry::GetFromExtension(const nsACString& aFileExt)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::GetFromExtension( aFileExt );
+    return nsGNOMERegistry::GetFromExtension( aFileExt );
+}
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsCommonRegistry::GetFromType(const nsACString& aMIMEType)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::GetFromType( aMIMEType );
+    return nsGNOMERegistry::GetFromType( aMIMEType );
+}
diff --git a/uriloader/exthandler/unix/nsCommonRegistry.h b/uriloader/exthandler/unix/nsCommonRegistry.h
new file mode 100644
index 000000000000..85b3d9cee25e
--- /dev/null
+++ b/uriloader/exthandler/unix/nsCommonRegistry.h
@@ -0,0 +1,28 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsCommonRegistry_h__
+#define nsCommonRegistry_h__
+
+#include "nsIURI.h"
+#include "nsCOMPtr.h"
+
+class nsMIMEInfoBase;
+
+class nsCommonRegistry
+{
+ public:
+  static bool HandlerExists(const char *aProtocolScheme);
+
+  static nsresult LoadURL(nsIURI *aURL);
+
+  static void GetAppDescForScheme(const nsACString& aScheme,
+                                  nsAString& aDesc);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromExtension(const nsACString& aFileExt);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromType(const nsACString& aMIMEType);
+};
+
+#endif
diff --git a/uriloader/exthandler/unix/nsKDERegistry.cpp b/uriloader/exthandler/unix/nsKDERegistry.cpp
new file mode 100644
index 000000000000..e3f3a07a9566
--- /dev/null
+++ b/uriloader/exthandler/unix/nsKDERegistry.cpp
@@ -0,0 +1,87 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsKDERegistry.h"
+#include "prlink.h"
+#include "prmem.h"
+#include "nsString.h"
+#include "nsMIMEInfoUnix.h"
+#include "nsAutoPtr.h"
+#include "nsKDEUtils.h"
+
+/* static */ bool
+nsKDERegistry::HandlerExists(const char *aProtocolScheme)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING( "HANDLEREXISTS" ));
+    command.AppendElement( nsAutoCString( aProtocolScheme ));
+    return nsKDEUtils::command( command );
+}
+
+/* static */ nsresult
+nsKDERegistry::LoadURL(nsIURI *aURL)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING( "OPEN" ));
+    nsCString url;
+    aURL->GetSpec( url );
+    command.AppendElement( url );
+    bool rv = nsKDEUtils::command( command );
+    if (!rv)
+      return NS_ERROR_FAILURE;
+
+    return NS_OK;
+}
+
+/* static */ void
+nsKDERegistry::GetAppDescForScheme(const nsACString& aScheme,
+                                     nsAString& aDesc)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING( "GETAPPDESCFORSCHEME" ));
+    command.AppendElement( aScheme );
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::command( command, &output ) && output.Length() == 1 )
+        CopyUTF8toUTF16( output[ 0 ], aDesc );
+}
+
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsKDERegistry::GetFromExtension(const nsACString& aFileExt)
+{
+    NS_ASSERTION(aFileExt[0] != '.', "aFileExt shouldn't start with a dot");
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING( "GETFROMEXTENSION" ));
+    command.AppendElement( aFileExt );
+    return GetFromHelper( command );
+}
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsKDERegistry::GetFromType(const nsACString& aMIMEType)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING( "GETFROMTYPE" ));
+    command.AppendElement( aMIMEType );
+    return GetFromHelper( command );
+}
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsKDERegistry::GetFromHelper(const nsTArray<nsCString>& command)
+{
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::command( command, &output ) && output.Length() == 3 )
+        {
+        nsCString mimetype = output[ 0 ];
+        RefPtr<nsMIMEInfoUnix> mimeInfo = new nsMIMEInfoUnix( mimetype );
+        NS_ENSURE_TRUE(mimeInfo, nullptr);
+        nsCString description = output[ 1 ];
+        mimeInfo->SetDescription(NS_ConvertUTF8toUTF16(description));
+        nsCString handlerAppName = output[ 2 ];
+        mimeInfo->SetDefaultDescription(NS_ConvertUTF8toUTF16(handlerAppName));
+        mimeInfo->SetPreferredAction(nsIMIMEInfo::useSystemDefault);
+        return mimeInfo.forget();
+        }
+    return nullptr;
+}
diff --git a/uriloader/exthandler/unix/nsKDERegistry.h b/uriloader/exthandler/unix/nsKDERegistry.h
new file mode 100644
index 000000000000..5b07eebc6d62
--- /dev/null
+++ b/uriloader/exthandler/unix/nsKDERegistry.h
@@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsKDERegistry_h__
+#define nsKDERegistry_h__
+
+#include "nsIURI.h"
+#include "nsCOMPtr.h"
+#include "nsTArray.h"
+
+class nsMIMEInfoBase;
+//class nsAutoCString;
+//class nsCString;
+
+class nsKDERegistry
+{
+ public:
+  static bool HandlerExists(const char *aProtocolScheme);
+
+  static nsresult LoadURL(nsIURI *aURL);
+
+  static void GetAppDescForScheme(const nsACString& aScheme,
+                                  nsAString& aDesc);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromExtension(const nsACString& aFileExt);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromType(const nsACString& aMIMEType);
+ private:
+  static already_AddRefed<nsMIMEInfoBase> GetFromHelper(const nsTArray<nsCString>& command);
+
+};
+
+#endif //nsKDERegistry_h__
diff --git a/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp b/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp
index 8ab279d1e79e..9558203ce59a 100644
--- a/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp
+++ b/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp
@@ -5,7 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsMIMEInfoUnix.h"
-#include "nsGNOMERegistry.h"
+#include "nsCommonRegistry.h"
 #include "nsIGIOService.h"
 #include "nsNetCID.h"
 #include "nsIIOService.h"
@@ -13,9 +13,12 @@
 #ifdef MOZ_ENABLE_DBUS
 #  include "nsDBusHandlerApp.h"
 #endif
+#if defined(XP_UNIX) && !defined(XP_MACOSX)
+#include "nsKDEUtils.h"
+#endif
 
 nsresult nsMIMEInfoUnix::LoadUriInternal(nsIURI* aURI) {
-  return nsGNOMERegistry::LoadURL(aURI);
+  return nsCommonRegistry::LoadURL(aURI);
 }
 
 NS_IMETHODIMP
@@ -28,15 +31,15 @@ nsMIMEInfoUnix::GetHasDefaultHandler(bool* _retval) {
   *_retval = false;
 
   if (mClass == eProtocolInfo) {
-    *_retval = nsGNOMERegistry::HandlerExists(mSchemeOrType.get());
+    *_retval = nsCommonRegistry::HandlerExists(mSchemeOrType.get());
   } else {
     RefPtr<nsMIMEInfoBase> mimeInfo =
-        nsGNOMERegistry::GetFromType(mSchemeOrType);
+        nsCommonRegistry::GetFromType(mSchemeOrType);
     if (!mimeInfo) {
       nsAutoCString ext;
       nsresult rv = GetPrimaryExtension(ext);
       if (NS_SUCCEEDED(rv)) {
-        mimeInfo = nsGNOMERegistry::GetFromExtension(ext);
+        mimeInfo = nsCommonRegistry::GetFromExtension(ext);
       }
     }
     if (mimeInfo) *_retval = true;
@@ -56,6 +59,23 @@ nsresult nsMIMEInfoUnix::LaunchDefaultWithFile(nsIFile* aFile) {
   nsAutoCString nativePath;
   aFile->GetNativePath(nativePath);
 
+  if( nsKDEUtils::kdeSupport()) {
+    bool supports;
+    if( NS_SUCCEEDED( GetHasDefaultHandler( &supports )) && supports ) {
+      nsTArray<nsCString> command;
+      command.AppendElement( NS_LITERAL_CSTRING( "OPEN" ));
+      command.AppendElement( nativePath );
+      command.AppendElement( NS_LITERAL_CSTRING( "MIMETYPE" ));
+      command.AppendElement( mSchemeOrType );
+      if( nsKDEUtils::command( command ))
+        return NS_OK;
+    }
+    if (!mDefaultApplication)
+      return NS_ERROR_FILE_NOT_FOUND;
+
+    return LaunchWithIProcess(mDefaultApplication, nativePath);
+  }
+
   nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
   if (!giovfs) {
     return NS_ERROR_FAILURE;
diff --git a/uriloader/exthandler/unix/nsOSHelperAppService.cpp b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
index 7e66e1e57dd3..42d80c0d5a71 100644
--- a/uriloader/exthandler/unix/nsOSHelperAppService.cpp
+++ b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
@@ -10,7 +10,7 @@
 #include "nsOSHelperAppService.h"
 #include "nsMIMEInfoUnix.h"
 #ifdef MOZ_WIDGET_GTK
-#  include "nsGNOMERegistry.h"
+#  include "nsCommonRegistry.h"
 #endif
 #include "nsISupports.h"
 #include "nsString.h"
@@ -1030,7 +1030,7 @@ nsresult nsOSHelperAppService::OSProtocolHandlerExists(
   if (!XRE_IsContentProcess()) {
 #ifdef MOZ_WIDGET_GTK
     // Check the GNOME registry for a protocol handler
-    *aHandlerExists = nsGNOMERegistry::HandlerExists(aProtocolScheme);
+    *aHandlerExists = nsCommonRegistry::HandlerExists(aProtocolScheme);
 #else
     *aHandlerExists = false;
 #endif
@@ -1050,7 +1050,7 @@ nsresult nsOSHelperAppService::OSProtocolHandlerExists(
 NS_IMETHODIMP nsOSHelperAppService::GetApplicationDescription(
     const nsACString& aScheme, nsAString& _retval) {
 #ifdef MOZ_WIDGET_GTK
-  nsGNOMERegistry::GetAppDescForScheme(aScheme, _retval);
+  nsCommonRegistry::GetAppDescForScheme(aScheme, _retval);
   return _retval.IsEmpty() ? NS_ERROR_NOT_AVAILABLE : NS_OK;
 #else
   return NS_ERROR_NOT_AVAILABLE;
@@ -1141,7 +1141,7 @@ already_AddRefed<nsMIMEInfoBase> nsOSHelperAppService::GetFromExtension(
 #ifdef MOZ_WIDGET_GTK
     LOG(("Looking in GNOME registry\n"));
     RefPtr<nsMIMEInfoBase> gnomeInfo =
-        nsGNOMERegistry::GetFromExtension(aFileExt);
+        nsCommonRegistry::GetFromExtension(aFileExt);
     if (gnomeInfo) {
       LOG(("Got MIMEInfo from GNOME registry\n"));
       return gnomeInfo.forget();
@@ -1253,7 +1253,7 @@ already_AddRefed<nsMIMEInfoBase> nsOSHelperAppService::GetFromType(
 
 #ifdef MOZ_WIDGET_GTK
   if (handler.IsEmpty()) {
-    RefPtr<nsMIMEInfoBase> gnomeInfo = nsGNOMERegistry::GetFromType(aMIMEType);
+    RefPtr<nsMIMEInfoBase> gnomeInfo = nsCommonRegistry::GetFromType(aMIMEType);
     if (gnomeInfo) {
       LOG(
           ("Got MIMEInfo from GNOME registry without extensions; setting them "
diff --git a/widget/gtk/moz.build b/widget/gtk/moz.build
index ae411457962e..993bd9386505 100644
--- a/widget/gtk/moz.build
+++ b/widget/gtk/moz.build
@@ -139,6 +139,7 @@ LOCAL_INCLUDES += [
     '/layout/style',
     '/layout/xul',
     '/other-licenses/atk-1.0',
+    '/toolkit/xre',
     '/widget',
     '/widget/headless',
 ]
diff --git a/widget/gtk/nsFilePicker.cpp b/widget/gtk/nsFilePicker.cpp
index 81ac66c30038..7d9451360ffd 100644
--- a/widget/gtk/nsFilePicker.cpp
+++ b/widget/gtk/nsFilePicker.cpp
@@ -9,6 +9,7 @@
 #include <unistd.h>
 
 #include <gtk/gtk.h>
+#include <gdk/gdkx.h>
 
 #include "nsGtkUtils.h"
 #include "nsIFileURL.h"
@@ -25,6 +26,7 @@
 #include "mozcontainer.h"
 
 #include "nsFilePicker.h"
+#include "nsKDEUtils.h"
 
 using namespace mozilla;
 
@@ -232,7 +234,9 @@ NS_IMETHODIMP
 nsFilePicker::AppendFilter(const nsAString& aTitle, const nsAString& aFilter) {
   if (aFilter.EqualsLiteral("..apps")) {
     // No platform specific thing we can do here, really....
-    return NS_OK;
+    // Unless it's KDE.
+    if( mMode != modeOpen || !nsKDEUtils::kdeSupport())
+      return NS_OK;
   }
 
   nsAutoCString filter, name;
@@ -342,6 +346,29 @@ nsFilePicker::Open(nsIFilePickerShownCallback* aCallback) {
   // Can't show two dialogs concurrently with the same filepicker
   if (mRunning) return NS_ERROR_NOT_AVAILABLE;
 
+  // KDE file picker is not handled via callback
+  if( nsKDEUtils::kdeSupport()) {
+    mCallback = aCallback;
+    mRunning = true;
+    NS_ADDREF_THIS();
+    g_idle_add([](gpointer data) -> gboolean {
+      nsFilePicker* queuedPicker = (nsFilePicker*) data;
+      int16_t result;
+      queuedPicker->kdeFileDialog(&result);
+      if (queuedPicker->mCallback) {
+        queuedPicker->mCallback->Done(result);
+        queuedPicker->mCallback = nullptr;
+      } else {
+        queuedPicker->mResult = result;
+      }
+      queuedPicker->mRunning = false;
+      NS_RELEASE(queuedPicker);
+      return G_SOURCE_REMOVE;
+    }, this);
+
+    return NS_OK;
+  }
+
   nsCString title;
   title.Adopt(ToNewUTF8String(mTitle));
 
@@ -577,6 +604,230 @@ void nsFilePicker::Done(void* file_chooser, gint response) {
   NS_RELEASE_THIS();
 }
 
+nsCString nsFilePicker::kdeMakeFilter( int index )
+    {
+    nsCString buf = mFilters[ index ];
+    for( PRUint32 i = 0;
+         i < buf.Length();
+         ++i )
+        if( buf[ i ] == ';' ) // KDE separates just using spaces
+            buf.SetCharAt( ' ', i );
+    if (!mFilterNames[index].IsEmpty())
+        {
+        buf += "|";
+        buf += mFilterNames[index].get();
+        }
+    return buf;
+    }
+
+static PRInt32 windowToXid( nsIWidget* widget )
+    {
+    GtkWindow *parent_widget = GTK_WINDOW(widget->GetNativeData(NS_NATIVE_SHELLWIDGET));
+    GdkWindow* gdk_window = gtk_widget_get_window( gtk_widget_get_toplevel( GTK_WIDGET( parent_widget )));
+    return GDK_WINDOW_XID( gdk_window );
+    }
+
+NS_IMETHODIMP nsFilePicker::kdeFileDialog(PRInt16 *aReturn)
+    {
+    NS_ENSURE_ARG_POINTER(aReturn);
+
+    if( mMode == modeOpen && mFilters.Length() == 1 && mFilters[ 0 ].EqualsLiteral( "..apps" ))
+        return kdeAppsDialog( aReturn );
+
+    nsCString title;
+    title.Adopt(ToNewUTF8String(mTitle));
+
+    const char* arg = NULL;
+    if( mAllowURLs )
+        {
+        switch( mMode )
+            {
+            case nsIFilePicker::modeOpen:
+            case nsIFilePicker::modeOpenMultiple:
+                arg = "GETOPENURL";
+                break;
+            case nsIFilePicker::modeSave:
+                arg = "GETSAVEURL";
+                break;
+            case nsIFilePicker::modeGetFolder:
+                arg = "GETDIRECTORYURL";
+                break;
+            }
+        }
+    else
+        {
+        switch( mMode )
+            {
+            case nsIFilePicker::modeOpen:
+            case nsIFilePicker::modeOpenMultiple:
+                arg = "GETOPENFILENAME";
+                break;
+            case nsIFilePicker::modeSave:
+                arg = "GETSAVEFILENAME";
+                break;
+            case nsIFilePicker::modeGetFolder:
+                arg = "GETDIRECTORYFILENAME";
+                break;
+            }
+        }
+
+  nsAutoCString directory;
+  if (mDisplayDirectory) {
+    mDisplayDirectory->GetNativePath(directory);
+  } else if (mPrevDisplayDirectory) {
+    mPrevDisplayDirectory->GetNativePath(directory);
+  }
+
+    nsAutoCString startdir;
+  if (!directory.IsEmpty()) {
+    startdir = directory;
+  }
+  if (mMode == nsIFilePicker::modeSave) {
+    if( !startdir.IsEmpty())
+      {
+      startdir += "/";
+      startdir += ToNewUTF8String(mDefault);
+      }
+    else
+      startdir = ToNewUTF8String(mDefault);
+  }
+
+    nsAutoCString filters;
+    PRInt32 count = mFilters.Length();
+    if( count == 0 ) //just in case
+        filters = "*";
+    else
+        {
+        filters = kdeMakeFilter( 0 );
+        for (PRInt32 i = 1; i < count; ++i)
+            {
+            filters += "\n";
+            filters += kdeMakeFilter( i );
+            }
+        }
+
+    nsTArray<nsCString> command;
+    command.AppendElement( nsAutoCString( arg ));
+    command.AppendElement( startdir );
+    if( mMode != nsIFilePicker::modeGetFolder )
+        {
+        command.AppendElement( filters );
+        nsAutoCString selected;
+        selected.AppendInt( mSelectedType );
+        command.AppendElement( selected );
+        }
+    command.AppendElement( title );
+    if( mMode == nsIFilePicker::modeOpenMultiple )
+        command.AppendElement( NS_LITERAL_CSTRING( "MULTIPLE" ));
+    if( PRInt32 xid = windowToXid( mParentWidget ))
+        {
+        command.AppendElement( NS_LITERAL_CSTRING( "PARENT" ));
+        nsAutoCString parent;
+        parent.AppendInt( xid );
+        command.AppendElement( parent );
+        }
+
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::commandBlockUi( command, GTK_WINDOW(mParentWidget->GetNativeData(NS_NATIVE_SHELLWIDGET)), &output ))
+        {
+        *aReturn = nsIFilePicker::returnOK;
+        mFiles.Clear();
+        if( mMode != nsIFilePicker::modeGetFolder )
+            {
+            mSelectedType = atoi( output[ 0 ].get());
+            output.RemoveElementAt( 0 );
+            }
+        if (mMode == nsIFilePicker::modeOpenMultiple)
+            {
+            mFileURL.Truncate();
+            PRUint32 count = output.Length();
+            for( PRUint32 i = 0;
+                 i < count;
+                 ++i )
+                {
+                nsCOMPtr<nsIFile> localfile;
+                nsresult rv = NS_NewNativeLocalFile( output[ i ],
+                                      PR_FALSE,
+                                      getter_AddRefs(localfile));
+                if (NS_SUCCEEDED(rv))
+                    mFiles.AppendObject(localfile);
+                }
+            }
+        else
+            {
+            if( output.Length() == 0 )
+                mFileURL = nsCString();
+            else if( mAllowURLs )
+                mFileURL = output[ 0 ];
+            else // GetFile() actually requires it to be url even for local files :-/
+                {
+                mFileURL = nsCString( "file://" );
+                mFileURL.Append( output[ 0 ] );
+                }
+            }
+  // Remember last used directory.
+  nsCOMPtr<nsIFile> file;
+  GetFile(getter_AddRefs(file));
+  if (file) {
+    nsCOMPtr<nsIFile> dir;
+    file->GetParent(getter_AddRefs(dir));
+    nsCOMPtr<nsIFile> localDir(do_QueryInterface(dir));
+    if (localDir) {
+      localDir.swap(mPrevDisplayDirectory);
+    }
+  }
+        if (mMode == nsIFilePicker::modeSave)
+            {
+            nsCOMPtr<nsIFile> file;
+            GetFile(getter_AddRefs(file));
+            if (file)
+                {
+                bool exists = false;
+                file->Exists(&exists);
+                if (exists) // TODO do overwrite check in the helper app
+                    *aReturn = nsIFilePicker::returnReplace;
+                }
+            }
+        }
+    else
+        {
+        *aReturn = nsIFilePicker::returnCancel;
+        }
+    return NS_OK;
+    }
+
+
+NS_IMETHODIMP nsFilePicker::kdeAppsDialog(PRInt16 *aReturn)
+    {
+    NS_ENSURE_ARG_POINTER(aReturn);
+
+    nsCString title;
+    title.Adopt(ToNewUTF8String(mTitle));
+
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING( "APPSDIALOG" ));
+    command.AppendElement( title );
+    if( PRInt32 xid = windowToXid( mParentWidget ))
+        {
+        command.AppendElement( NS_LITERAL_CSTRING( "PARENT" ));
+        nsAutoCString parent;
+        parent.AppendInt( xid );
+        command.AppendElement( parent );
+        }
+
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::commandBlockUi( command, GTK_WINDOW(mParentWidget->GetNativeData(NS_NATIVE_SHELLWIDGET)), &output ))
+        {
+        *aReturn = nsIFilePicker::returnOK;
+        mFileURL = output.Length() > 0 ? output[ 0 ] : nsCString();
+        }
+    else
+        {
+        *aReturn = nsIFilePicker::returnCancel;
+        }
+    return NS_OK;
+    }
+
 // All below functions available as of GTK 3.20+
 void* nsFilePicker::GtkFileChooserNew(const gchar* title, GtkWindow* parent,
                                       GtkFileChooserAction action,
diff --git a/widget/gtk/nsFilePicker.h b/widget/gtk/nsFilePicker.h
index 00b1520e827b..50169a0f9fe8 100644
--- a/widget/gtk/nsFilePicker.h
+++ b/widget/gtk/nsFilePicker.h
@@ -72,6 +72,12 @@ class nsFilePicker : public nsBaseFilePicker {
  private:
   static nsIFile* mPrevDisplayDirectory;
 
+  bool kdeRunning();
+  bool getKdeRunning();
+  NS_IMETHODIMP kdeFileDialog(PRInt16 *aReturn);
+  NS_IMETHODIMP kdeAppsDialog(PRInt16 *aReturn);
+  nsCString kdeMakeFilter( int index );
+
   void* GtkFileChooserNew(const gchar* title, GtkWindow* parent,
                           GtkFileChooserAction action,
                           const gchar* accept_label);
diff --git a/xpcom/components/ManifestParser.cpp b/xpcom/components/ManifestParser.cpp
index 29f30560c45a..61dcb19696df 100644
--- a/xpcom/components/ManifestParser.cpp
+++ b/xpcom/components/ManifestParser.cpp
@@ -38,6 +38,7 @@
 #include "nsIScriptError.h"
 #include "nsIXULAppInfo.h"
 #include "nsIXULRuntime.h"
+#include "nsKDEUtils.h"
 
 using namespace mozilla;
 
@@ -398,6 +399,7 @@ void ParseManifest(NSLocationType aType, FileLocation& aFile, char* aBuf,
   NS_NAMED_LITERAL_STRING(kOs, "os");
   NS_NAMED_LITERAL_STRING(kOsVersion, "osversion");
   NS_NAMED_LITERAL_STRING(kABI, "abi");
+  NS_NAMED_LITERAL_STRING(kDesktop, "desktop");
   NS_NAMED_LITERAL_STRING(kProcess, "process");
 #if defined(MOZ_WIDGET_ANDROID)
   NS_NAMED_LITERAL_STRING(kTablet, "tablet");
@@ -453,6 +455,7 @@ void ParseManifest(NSLocationType aType, FileLocation& aFile, char* aBuf,
   }
 
   nsAutoString osVersion;
+  nsAutoString desktop;
 #if defined(XP_WIN)
 #  pragma warning(push)
 #  pragma warning(disable : 4996)  // VC12+ deprecates GetVersionEx
@@ -461,14 +464,17 @@ void ParseManifest(NSLocationType aType, FileLocation& aFile, char* aBuf,
     nsTextFormatter::ssprintf(osVersion, u"%ld.%ld", info.dwMajorVersion,
                               info.dwMinorVersion);
   }
+  desktop = NS_LITERAL_STRING("win");
 #  pragma warning(pop)
 #elif defined(MOZ_WIDGET_COCOA)
   SInt32 majorVersion = nsCocoaFeatures::OSXVersionMajor();
   SInt32 minorVersion = nsCocoaFeatures::OSXVersionMinor();
   nsTextFormatter::ssprintf(osVersion, u"%ld.%ld", majorVersion, minorVersion);
+  desktop = NS_LITERAL_STRING("macosx");
 #elif defined(MOZ_WIDGET_GTK)
   nsTextFormatter::ssprintf(osVersion, u"%ld.%ld", gtk_major_version,
                             gtk_minor_version);
+  desktop = nsKDEUtils::kdeSession() ? NS_LITERAL_STRING("kde") : NS_LITERAL_STRING("gnome");
 #elif defined(MOZ_WIDGET_ANDROID)
   bool isTablet = false;
   if (mozilla::AndroidBridge::Bridge()) {
@@ -476,6 +482,7 @@ void ParseManifest(NSLocationType aType, FileLocation& aFile, char* aBuf,
         "android/os/Build$VERSION", "RELEASE", osVersion);
     isTablet = java::GeckoAppShell::IsTablet();
   }
+  desktop = NS_LITERAL_STRING("android");
 #endif
 
   if (XRE_IsContentProcess()) {
@@ -572,6 +579,7 @@ void ParseManifest(NSLocationType aType, FileLocation& aFile, char* aBuf,
     TriState stTablet = eUnspecified;
 #endif
     int flags = 0;
+    TriState stDesktop = eUnspecified;
 
     while ((token = nsCRT::strtok(whitespace, kWhitespace, &whitespace)) &&
            ok) {
@@ -581,6 +589,7 @@ void ParseManifest(NSLocationType aType, FileLocation& aFile, char* aBuf,
       if (CheckStringFlag(kApplication, wtoken, appID, stApp) ||
           CheckOsFlag(kOs, wtoken, osTarget, stOs) ||
           CheckStringFlag(kABI, wtoken, abi, stABI) ||
+          CheckStringFlag(kDesktop, wtoken, desktop, stDesktop) ||
           CheckStringFlag(kProcess, wtoken, process, stProcess) ||
           CheckVersionFlag(kOsVersion, wtoken, osVersion, stOsVersion) ||
           CheckVersionFlag(kAppVersion, wtoken, appVersion, stAppVersion) ||
@@ -627,7 +636,7 @@ void ParseManifest(NSLocationType aType, FileLocation& aFile, char* aBuf,
     }
 
     if (!ok || stApp == eBad || stAppVersion == eBad ||
-        stGeckoVersion == eBad || stOs == eBad || stOsVersion == eBad ||
+        stGeckoVersion == eBad || stOs == eBad || stOsVersion == eBad || stDesktop == eBad ||
 #ifdef MOZ_WIDGET_ANDROID
         stTablet == eBad ||
 #endif
diff --git a/xpcom/components/moz.build b/xpcom/components/moz.build
index f9a536cf48de..09f5a89bb56a 100644
--- a/xpcom/components/moz.build
+++ b/xpcom/components/moz.build
@@ -71,6 +71,7 @@ LOCAL_INCLUDES += [
     '/js/xpconnect/loader',
     '/layout/build',
     '/modules/libjar',
+    '/toolkit/xre',
 ]
 
 if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
diff --git a/xpcom/io/nsLocalFileUnix.cpp b/xpcom/io/nsLocalFileUnix.cpp
index 6d6b22e7e583..95b5fce15f63 100644
--- a/xpcom/io/nsLocalFileUnix.cpp
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -52,6 +52,7 @@
 
 #ifdef MOZ_WIDGET_GTK
 #  include "nsIGIOService.h"
+#  include "nsKDEUtils.h"
 #endif
 
 #ifdef MOZ_WIDGET_COCOA
@@ -1910,18 +1911,16 @@ nsLocalFile::Reveal() {
   }
 
 #ifdef MOZ_WIDGET_GTK
-  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
-  if (!giovfs) {
-    return NS_ERROR_FAILURE;
-  }
+  nsAutoCString url;
 
   bool isDirectory;
   if (NS_FAILED(IsDirectory(&isDirectory))) {
     return NS_ERROR_FAILURE;
   }
 
+  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
   if (isDirectory) {
-    return giovfs->ShowURIForInput(mPath);
+    url = mPath;
   }
   if (NS_SUCCEEDED(giovfs->OrgFreedesktopFileManager1ShowItems(mPath))) {
     return NS_OK;
@@ -1935,7 +1934,7 @@ nsLocalFile::Reveal() {
     return NS_ERROR_FAILURE;
   }
 
-  return giovfs->ShowURIForInput(dirPath);
+  url = dirPath;
 #elif defined(MOZ_WIDGET_COCOA)
   CFURLRef url;
   if (NS_SUCCEEDED(GetCFURL(&url))) {
@@ -1947,6 +1946,17 @@ nsLocalFile::Reveal() {
 #else
   return NS_ERROR_FAILURE;
 #endif
+  if(nsKDEUtils::kdeSupport()) {
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING("REVEAL") );
+    command.AppendElement( mPath );
+    return nsKDEUtils::command( command ) ? NS_OK : NS_ERROR_FAILURE;
+  }
+
+  if (!giovfs)
+    return NS_ERROR_FAILURE;
+
+  return giovfs->ShowURIForInput(url);
 }
 
 NS_IMETHODIMP
@@ -1956,6 +1966,12 @@ nsLocalFile::Launch() {
   }
 
 #ifdef MOZ_WIDGET_GTK
+  if( nsKDEUtils::kdeSupport()) {
+    nsTArray<nsCString> command;
+    command.AppendElement( NS_LITERAL_CSTRING("OPEN") );
+    command.AppendElement( mPath );
+    return nsKDEUtils::command( command ) ? NS_OK : NS_ERROR_FAILURE;
+  }
   nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
   if (!giovfs) {
     return NS_ERROR_FAILURE;
-- 
2.25.1