I've been using the new Firefox 3.0 browser for several days now and I have to say that I am very impressed with it.
The browser certainly feels substantially faster at loading the same pages that I frequently visited before with Firefox 2 and with Internet Explorer 7 -- though I have to admit that this is very subjective and that server and ISP performance come into play.
I was a bit concerned that the browser address bar no longer indicates the SSL status of the site I'm visiting. This was a conscious decision by Firefox developers and there are work-arounds for getting it back. I'm not sure I agree with the arguments either way yet, but I was a bit surprised when I first went to a site and the SSL status was no longer indicated in the address bar -- I had to go checking a bit to make sure I was where I thought I was.
The problem that drove this change was the fact that they are now indicating site status with the background around the site icon that shows to the left of the location bar and the colors for the three states (unsecure, ssl and ev) did not match the colors of the address background. The ultimate decision was to leave the address bar uncolored and solely rely on the icon background. While I agree that if there are colors on the background that they must be the same, I think I disagree with not also reflecting the colors on the address background as well. You can read more about this change and the logic/discussion behind it here.
The only problem I've observed so far is that the ordering process at the AT&T wireless site does not work (my son lost his phone and I had to order a replacement for him). I can't explain clearly what the problem is as the site just behaved incorrectly -- asking me for the same information multiple times or doing other strange things like showing nothing in the cart after I selected a phone, clicked on add-to-cart and the popup that resulted from that operation would show that no phone was put into the cart). I tried logging out and logging back in and restarting the browser -- all to no avail. I ended up having to use Internet Explorer to make the order.
Overall, I'm very satisfied with the new version of Firefox and recommend that others using earlier versions of upgrade -- you will like the speed improvements. Congrats Firefox team on a great upgrade!