Heres a nice little addon i just found. It allows you to use uncompatable addons with firefox 3. Now note, there is some instability, but ive tested with a few things and works great. Heres the link: Oxymoronical ยป Nightly Tester Tools
Just in your addons section click ignore compatablility, have fun, and make sure you dont over do it, cause to much instability can cause crashes