After nearly a day living with the new Firefox, it's very nice. Very, very nice.
I must admit that Firefox 2 often frustrated me, crashing at inopportune moments. (I can break anything.) So far (knock on wood) Firefox 3 is sailing through like a champ.
One thing I often do is bring up a host of tabs while writing a story, as many as two dozen. Firefox 2 hiccuped badly. Firefox 3 seems to handle it.
Firefox 2 would sometimes forget that I like big text for these old eyes. Firefox 3 hasn't forgotten yet. (This is now called the Zoom feature. It used to be called increase or decrease text size.)
One reason I was reluctant to be a beta-tester for Firefox 3 was because I have add-ons, some of which I paid for, and the beta versions did not support them. It took me five minutes to get them working in Firefox 3.
There are new security settings on the Advanced tab under Tools, which are very, very nice. I especially like being warned if the page tries to re-load -- a favorite phisher trick foiled.
You can customize the controls on toolbars through a single screen accessed from the View menu. The Page Source under View is also very clear now -- makes it easy to see how pages are made.
Entering unfamiliar Web pages is now easier. As soon as you start entering an address, the new Firefox starts guessing at your meaning. Keep typing and it's bound to guess right, so you click on that entry and don't go wrong.
Overall, I'd say that if you like Firefox 2 you want to upgrade to Firefox 3 pretty quickly. That's rare praise. Great job, guys.