Modern-ThunderBird

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

Updated tabs and toolbar

Updated dropdown menus

Works with dark theme

Works with light theme

Works with custom themes (also URL bar is fixed)

Installation

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.
   • Linux (Flatpak) - $HOME/.var/app/org.mozilla.Thunderbird/.thunderbird/b96p321h.default-XXXXXX
   • Windows 10 - C:\Users\<USERNAME>\AppData\Roaming\Thunderbird\Profiles\XXXXXXX.default-XXXXXX.
   • MacOS - Users/<USERNAME>/Library/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.

Other Settings

You may notice that your thunderbird doesn't quite look like the first screenshot. To fix this, go to Menu > View > Density and set it to "Touch". Then change the font size to 12px

End of Useful Life

You might have heard about the upcoming release of Thunderbird Supernova some time in 2023. Based on the screenshots, it seems like it may do away with tabs all together, so this theme may no longer serve much of a purpose after that point.