I installed Firefox 3 Beta 5 the other day, and I've had a few good days to play around with it. So far the experience has been great. There have been a few extension problems that have caused the browser to crash, but that's probably because I'm forcing certain older extensions to run on the beta, or running beta versions of extensions myself. Even while it's still in beta I wouldn't go back to FF2. It's that good.
Firstly the performance side of things. You've probably heard a lot about this from other blogs, and it's all true. The program is a lot quicker. Leaving it open over night doesn't result in a daily restart of Firefox (yay). Tabs appear to load quicker and I no longer have the tab stalling issue I previously had (loading content in a tab froze the program for a few seconds).
The UI changes have been subtle and over all it's a improvement. It's still consistent with the FF2 UI so don't expect many changes.
The main thing I wanted to point out is the new address bar. In FF2 you used the address bar to type in urls, and if your url matched a previously visited site, it also displayed a list of matching urls in a list under the address bar. Firefox 3 takes this to the next level. You can now search your history/bookmarks from the address bar. The search functionality includes the page title, parts of the url (not the start of the url like FF2). I love the idea of this, however I'm still getting used to it. I'm so used to typing in urls that I only realise after I've opened the site that it would have been quicker to type part of the name. Getting to phpmyadmin by typing
phpm instead of
localhost/phpmyadmin is a lot quicker!
There are plenty of other changes I love about Firefox3, but I just wanted to point out a few. I would strongly suggest that if you use Firefox 2 to at least read up on Firefox 3. If your game try installing the Beta, I'm sure you wont go back.