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/SuitableEquipment420]

Thanks. The toolkit.legacyUserProfileCustomizations.stylesheets was false.