Firefox 3 release candidate 1 is out, and you can download it here. If you use firebug a lot, it might be worth holding onto v2 for a bit*, otherwise I’d strongly recommend switching to 3. I’ve only run RC1 in linux (at work and home), and so far it’s been exceptional. It runs faster, looks great, and is good for you.
I had previously complained about the visual complexity of the location bar (aka awesome bar). For some reason, it no longer bothers me. I think it’s partly because of small UI changes, but mostly that I’ve become used to it.
One thing I’m finding especially useful with the awesome bar: Gmail has the subject of the message you’re reading in the title, so if you’ve read a message before and want to find it, you can search your messages without even going into gmail, just start typing words from the subject in the awesome bar. Even more useful is with things like Google Docs. If you have a spreadsheet that you open every once in a while, just type the name of the spreadsheet in, and the (cryptic) URL will come up. MAGIC.
I wonder if this will affect the way that website developers create titles and URLs for pages. The value of unique, memorable titles for pages has just increased.
Dria.org has good overviews of a lot of the changes from 2 to 3 (with pictures!).
* You can run firebug with FF3RC1, you just need to run the alpha last I checked, and it isn’t terribly stable yet.