Did you make sure that the file is in the correct profile folder and that the file doesn't have a hidden .txt or .css file extension and that you still have enabled this file via about:config ? See his thread for recent code: *[[/questions/1305615]] tabs below address bar - an ongoing problem not fixed !!! ---- It is not that difficult to create <b>userChrome.css</b> if you have never used it. The first step is to open the "Help -> Troubleshooting Information" page and find the button to access the profile folder. *https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox You can find this button under the "Application Basics" section as "Profile Folder -> Open Folder". If you click this button then you open the profile folder in the Windows File Explorer. You need to create a folder with the name <u>chrome</u> in this folder (name is all lowercase). In the <b>chrome</b> folder you need to create a plain text file with the name <b>userChrome.css</b> (name is case sensitive). In this userChrome.css text file you paste the text posted. On Mac you can use the TextEdit utility to create the userChrome.css file as a plain text file. In Windows saving the file is usually the only time things get more complicated because Windows can silently add a .txt file extension and you end up with a file named <i>userChrome.css.txt</i>. To avoid this you need to make sure to select "All files" in the dialog to save the file in the text editor using "Save File as". You need to close (Quit/Exit) and restart Firefox when you create or modify the userChrome.css file. See also: *https://www.userchrome.org/what-is-userchrome-css.html *https://www.userchrome.org/how-create-userchrome-css.html In Firefox 69 and later you need to set this pref to true on the <b>about:config</b> page to enable userChrome.css and userContent.css in the chrome folder. *toolkit.legacyUserProfileCustomizations.stylesheets = true See: *https://www.userchrome.org/firefox-changes-userchrome-css.html