I've just been reminded of another extension that can come in handy. User Agent Switcher.

Sometimes a web site will want particular browser(s) but will work with others. UserAgent switcher, will make firefox appear to be a different browser. In the case that has just reminded me, the user wanted video from Fox News. That site gives:

Windows 2000, Windows XP, Windows XP Media Center 2005, Mac OSX 10.3 or Mac OSX 10.4 is required to view this page

but telling it your firefox browser is IE7 on Vista will make the video available.