UserChrome.css
From MozillaZine Knowledge Base
userChrome.css in the chrome folder is a CSS file that can be used to change the way Mozilla applications' interfaces look. This file does not exist in a new profile.
Editing
This file is meant to be edited manually. Anything valid in a CSS file is valid in this file. The application must be restarted for changes to take effect (to get around this, you could use the Stylish extension). For sample styles, see:
- userstyles.org
- Firefox Help: Tips & Tricks: Browser Appearance
- Category:Visual customizations (Firefox)
Moving
This file can be moved to a different profile. If it contains imports or references to other files such as images, these files should be moved along with it.
Deleting
Deleting userChrome.css will get rid of any user styles defined upon restart.