Firefox 4 - make the app menu transparent

To change the "Firefox" app menu from orange to transparent in Firefox 4, edit your <profile>/chrome/userChrome.css thus:

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul); 

#appmenu-button{

    background:transparent!important;

}

source: http://www.lifehacker.com.au/2011/03/from-the-tips-box-windows-7-favorites-the-firefox-button/