userChrome.js allows to easily customize Firefox through JavaScript.

What userChrome.css is for CSS customization, userChrome.js is for JavaScript. Simply edit the file userChrome.js (in the same place as userChrome.css) and its content will be run whenever a new browser window is opened (onLoad). BTW: If you want this to become a standard part of Firefox in the future, go and post a patch to bug 332529.


Note: This extension has been superceded by the userChromeJS extension. See its homepage for any support.

userChrome.js 0.8 [released 2007-06-07, updated 2008-10-26]

This release should work for Firefox and Thunderbird 2.0 and 3.0 as well as all Gecko 1.9 applications such as Seamonkey 2.0, Flock 2.0, Songbird 1.0, Fennec, etc.

Sample code

Basics (should work for most applications):

Extension replacements (for Firefox 3.0 and 3.5)


Version 0.8
userChrome.js is now run for every chrome window, not just the main one
Suggested for inclusion into one of the next Firefox versions (see bug 332529)
Version 0.7
Added support for most current Gecko applications
Version 0.6
The file userChrome.js is automatically created
Version 0.5
Initial release (2006-01-24)
Logo of zeniko's webcreations