A userChrome.css theme to make thunderbird resemble Firefox 89+

  • By scanunicco
  • Last update: Dec 8, 2022
  • Comments: 2


A userChrome.css theme to make Thunderbird (78+) resemble Firefox 89+

Updated tabs and toolbar Updated tabs and toolbar

Updated dropdown menus Updated dropdown menus

Works with themes Works with most themes other than the default light theme.


  1. Download the file named userChrome.css from this repo.

  2. Open Preferences and scroll all the way to the bottom of the General tab.

  3. Click Config Editor...

  4. A dialog will warn you, but ignore it, press the I accept the risk! button.

  5. Enable the following flags by right clicking and selecting toggle:

    • toolkit.legacyUserProfileCustomizations.stylesheets
  6. Go to your Thunderbird profile.

    • Linux - $HOME/.thunderbird/XXXXXXX.default-XXXXXX/.
    • Windows 10 - C:\Users\<USERNAME>\AppData\Roaming\Thunderbird\Profiles\XXXXXXX.default-XXXXXX.
    • macOS - Users/<USERNAME>/Library/Application Support/Thunderbird/Profiles/XXXXXXX.default-XXXXXXX.
  7. Create a folder and name it chrome, then copy userChrome.css from step 1 to chrome folder.

  8. Restart Thunderbird.




  • 1

    Shadow on tab is missing

    Hi, this css of thunderbird is grate, but in firefox there is a light shadow in selected tab, may be you can add this style in the userChrome.css

    .tab-background[selected="true"] { box-shadow: 0px 0px 4px #888888; }

  • 2

    Different MacOS Installation Location

    This is really well done, thank you for creating some continuity between Firefox and Tunderbird.

    For me on MacOS, the location that I had to place chrome/userChrome.css in was Users/<USERNAME>/Library/Thunderbird/Profiles/XXXXXXX.default-XXXXXXX not Users/<USERNAME>/Library/Application Support/Thunderbird/Profiles/XXXXXXX.default-XXXXXXX.