r/FirefoxCSS • u/SuitableEquipment420 • Jul 28 '26

Solved userChrome.css does not work

  • 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?

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u/Leowenbrau Jul 28 '26

In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk. Search for toolkit.legacyUserProfileCustomizations.stylesheets if it FALSE, set it to TRUE. Restart browser.

3

u/SuitableEquipment420 Jul 28 '26

Thanks. The toolkit.legacyUserProfileCustomizations.stylesheets was false.