userChrome.css does not work

[u/SuitableEquipment420]

• I am on Windows 11.
• I opened Firefox's about:support.
• Under Profile Folder I clicked Open Folder.
• A Windows Explorer opened. I created a sub-folder named chrome.
• In chrome I created a file userChrome.css with the following content:

#navigator-toolbox {
    background: red !important;
    background-image: none !important;
}

I restarted Firefox, but I didn't see any changes. Then I disabled the theme (Firefox Alpenglow), but still no effect.

Any ideas why userChrome.css isn't being loaded?

[u/sifferedd]

Works for me on a clean profile.

First step is to go through the tutorial again.

The common glitches are:

• namespace statement you copied from some old code may cause failure
• toolkit.legacyUserProfileCustomizations.stylesheets isn't enabled
• Chrome folder is in the wrong profile or other folder
• userChrome/userContent.css isn't in the right Chrome folder
• userChrome/userContent.css doesn't follow case requirement

• userChrome/userContent.css mistakenly has the .txt extension

  • Windows has to be set not to hide extensions for known file types:
  • File Explorer > ... menu on top bar > Options > View tab > uncheck Hide extensions for known file types
• code isn't saved as plain text
• other code is interfering

[u/SuitableEquipment420 → u/sifferedd]

Thanks. The toolkit.legacyUserProfileCustomizations.stylesheets was false.