From: Jory A. Pratt <anarchy@gentoo.org>

Install the Gentoo preference file into the omni.jar

diff --git a/browser/installer/package-manifest.in b/browser/installer/package-manifest.in
--- a/browser/installer/package-manifest.in
+++ b/browser/installer/package-manifest.in
@@ -649,16 +649,17 @@
 ; updater icon
 @RESPATH@/icons/updater.png
 #endif
 #endif
 #endif
 
 ; [Default Preferences]
 ; All the pref files must be part of base to prevent migration bugs
+@RESPATH@/browser/@PREF_DIR@/all-gentoo.js
 @RESPATH@/browser/@PREF_DIR@/firefox.js
 @RESPATH@/browser/@PREF_DIR@/firefox-branding.js
 @RESPATH@/greprefs.js
 @RESPATH@/defaults/autoconfig/prefcalls.js
 @RESPATH@/browser/defaults/permissions
 @RESPATH@/browser/defaults/blocklists
 @RESPATH@/browser/defaults/pinning