I got an email today from a Zoner who upgraded to FireFox 3, and reports serious problems, notably the page reduced to a small window in the browser instead of taking up 100% of the space.
I need reports from FF3 users to get a handle on this, so please let me know the good or bad.
My advice: Never go for the first release of a major upgrade. N.0 will get you every time, either because of undiscovered bugs, or because of incompatibilities that will take time for third-parties to fix. Let some other sucker take the heat.