userChrome.jsuserChrome.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
