How do I set Firefox to use a custom theme for all new users?

Solution 1:

Step 1: Download the theme file

Go to Firefox Themes website and download the xpi file of your favorite theme, say Arc Theme.

Step 2: Install the theme for all users

Open the downloaded theme file with Archive Manager.

You'll see an install.rdf file inside. Open it too and copy the ID between the first <em:id> and</em:id> you find, which in Arc Theme's case is {52c2877e-44e1-11e5-8874-a62d1d5d46B0}. Note the theme's internal name too, you'll need it later.

Rename the theme's xpi file with the ID you just copied. Then place the renamed xpi file in /usr/lib/firefox-addons/extensions/. To do so, open the Terminal and run this command:

pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY nautilus /usr/lib/firefox-addons/extensions/

and copy the xpi file ({52c2877e-44e1-11e5-8874-a62d1d5d46B0}.xpi in Arc Theme's case) to the File Manager window that opens up.

Step 3: Set the theme as default

Create a theme.js file (or a .js file with any name you like) in /usr/lib/firefox/browser/defaults/preferences/. To do so, open the Terminal and run this command:

pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY gedit /usr/lib/firefox/browser/defaults/preferences/theme.js

When the preferences file gets opened in Text Editor, copy and paste this into it:

pref("general.skins.selectedSkin", "arc-theme");

But, don't forget to replace arc-theme with the theme's internal name you saw in install.rdf! 😊

Okay, that's all. Firefox is now set to use your favorite theme by default!😃 Tested and verified on Ubuntu 14.04LTS with Firefox 45.

Background

Solus Project uses Firefox as it's default browser, but with it's theme set to Arc Darker 'out of box'. So, I poked around their firefox and arc-firefox-theme packages, found out how it works and then reproduced the method on Ubuntu. 😎