How to Create a userChrome.css File
Updated May 24, 2019; Originally posted by jscher2000 on November 5, 2017.
Creating your userChrome.css file is the first step on your quest to make over Firefox’s interface. It takes a couple of minutes, but it’s important to take your time and get it right so Firefox loads and applies your style recipes on the first try.
At startup, Firefox will check for the userChrome.css file in a particular location: a folder named chrome inside your currently active profile folder. The profile folder is where all of your current settings and add-ons are stored. (If you want to learn more about that folder, see “Profiles — Where Firefox stores your bookmarks, passwords and other user data” on Mozilla Support.)
Here’s how you set that up (full details below):
- Open your currently active profile folder
- Create a new folder named chrome
- Create a desktop shortcut (alias) to the chrome folder for easier future access
- Make sure your OS is set to show you file extensions like .txt and .css
- Create a new text file inside the chrome folder named userChrome.css
- Change a preference in Firefox so it looks for your files at startup (in Firefox 69+)