FireFox 3 Upgrade Notes
Plugin update check doesn't work for a number of plugins (in particular: FireBug and Web Developer.)
You can get FireBug to work by visiting getfirebug.com and downloading the 1.1 beta.
Get Web Developer to work by visiting the web developer plugin page. While, you're doing that, visit Chris Pederick's home page and click on an ad. It's the least you can do.
My first impression of the latest beta (b4) is that it seems very fast page rendering. Maybe as fast as Safari.