FireFox 1.5, good
berkeley
I installed FireFox 1.5 this morning and have been using it all day. It's a pretty sweet user experience.
It seems much more stable than the 1.0.x line and positively smokes when it comes to speed. To upgrade, I followed the instructions I've developed here: "How to upgrade FireFox on the Mac, 100% Clean". I did use one modification to those instructions to get older extensions to run: "Make old extensions work with new FireFox". GMail seems especially faster.
Let me know if those instructions don't work for you (they are written in a mac-like way, but should be more generally applicable to PCs; I think).