Having problems with your add-ons not working in the latest Firefox betas? The solution is simple: Nightly Tester Tools

The only add-on that doesn’t work for me is TabGroups, due to it not being able to do a secure update (which I guess is a good thing, the Firefox team have stepped up security on add-ons).

I also recommend using the Portable version of the Firefox 3 beta, as if anything happens, it won’t affect any of your current profiles you have on the previous installs of Firefox.