Using older addons in Firefox 3.0 beta 
So I've been playing around with
Firefox 3.0b5 for the last few weeks now and it really rocks! It seems to have become quite the speed daemon. Unfortunately, there's quite a few extensions which haven't yet been ported to work on the new version. Luckily I came across the following tip which disables compatibility checking for firefox so you can install the old extensions. All the extensions I use appear to work fine in 3.0b5.
http://lifehacker.com/355973/make-your-extensions-work-with-the-firefox-3-beta