Firefox This is a set of patches to make firefox work better with dark themes.  It is not a Firefox theme.
Unpack the Menda Dark package and locate the Firefox chrome folder.  Next go to '~/.mozilla/firefox/xSomeNumbers.default'.
If there is no 'chrome' folder, just copy and paste the one from inside the Menda Dark theme folder.
If there is a 'chrome' folder, merge its contents with the Medna Dark 'chrome' folder.
Restart Firefox to apply the theme.  This theme depends on Menda Dark being in use to work properly!

User Profile You may also desire to create a new user-porfile for the Menda Dark theme since it hard codes its appearance.  To do this simply open firefox with a trailing '-p', for example: firefox -p.  A small gui will appear.  Choose create profile and follow the instructions.  If you would like this gui to appear at every start-up(recommended) so you can choose you profile.  Un-tick 'Don't ask at startup', or you can always start the app with the '-p' to change profiles again.

AneX