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).

If you want this to become a standard part of Firefox in the future, go and vote for bug 332529 and/or contribute to the discussion about how to fix this.

Download

userChrome.js 0.8 [released 2007-06-07]

This release should work for Firefox and Thunderbird 2.0 as well as version 1.5.0.7 and later and all Gecko 1.9 applications such as Firefox 3 nightlies.

In case you're using an older version of the above or a different Gecko application such as SeaMonkey, Netscape, Flock, etc., you'll have to install version 0.7.