Firefox/Thunderbird - Change Active Tab Colour

This procedure will change the colour of the active tab in Firefox(v59+) or Thunderbird(v60+). The procedure is essentially the same for both Firefox and Thunderbird.

Make sure that your "file explorer" is configured to show "hidden folders". (top menu, file, view, select "Hidden items on the right)

First - Ensure that you have a theme (Dark or Light) selected. This procedure has no effect on the Default Theme!

For Firefox v69+ you need to enable userChrome.css. about:config and set "toolkit.legacyUserProfileCustomizations.stylesheets" to true

  1. Go to your
  2. Open your profile folder. If there is more than one profile use the one with the latest date.(should be something.default or default-release ie fhty6gbo.default.release)
  3. Using Notepad or similar editor create a file named userChrome.css

Change the rgb(220, 53, 84) colour to suit.

Quite simple. Took me quite a bit of time to figure this out.

Firefox/Thunderbird - Change App Text Size

  1. Open configuration file
  2. Search:Pix
  3. layout.css.devPixelsPerPx
  4. Modify value - Try 1.12 or 1.25 - be careful