Inside this folder is the userChrome.css file. In the folder that opens, look for a folder called ‘Chrome’. Go to about:support and scroll down to the profile row. You have to modify the userChrome.css file in order to get colored title bars in Firefox. If you’re running anything older than Firefox 40, you can use the old hack. Unfortunately, Firefox 40 removed this file and the hack became obsolete. Here’s how you can get colored title bars in Firefox, regardless which version of the browser you’re running. A hack for the shortcoming was quickly developed by modifying the userChrome.css file. Once it was added though, Firefox choose to sit the feature out. Users resorted to UI modifying apps and themes to get colored title bars until the feature was added natively. Initially, title bars in Windows 10 had no color. Firefox never added support for colored title bars in Windows 10.
