Updated May 10 - (See end of story)
A few weeks ago, there was an announcement from Mozilla that Firefox 3.0 (even though still in Beta) was 'safe' for public use. That may have been a little premature.
Lots of add-ons are just making the 3.0 cut now, and there a still just a few issues being 'knocked off' by a very dedicated team.
Firefox 18.104.22.168 is still the stable release and can be downloaded here.
Firefox 3.0 Beta 5 is making GREAT progress in many of the nightly builds.
After seeing a few troubled comments the past few days (mostly from people on the Apple platform), I thought it was time to point some stuff out.
1) It's probably not Firefox that's the culprit but a setting you've chosen in the browser preferences (or a huge, unnecessary cache).
2) Switching to Flock shouldn't make a difference at all since Flock is using the 'stable' Gecko engine (the same one used in Firefox 2.0)
(Sidenote: You can help! Check out this Mozilla page.)
A word about 'nightly builds'. For the most part, they're put out there for the developers. They're test builds of the latest browser rendition and although most show improvement, you could catch one that's off the mark. Be careful if you're messing with these.
Overall (Yes, I download them), Firefox 3 Beta 5 is showing really great promise and no doubt will debut 'stable' well before Internet Explorer 8 does.
Speaking of Internet Explorer, if you upgrade to the new Windows XP Service Pack 3 and already are using IE7, you will not be able to uninstall it. More on that (and IE8's progress) here.
As noted previously, Flock is just cool if you're doing 'the social thing' and Apple's Safari for Windows does a good job displaying your website or blog as it would appear on a Mac (and it's quick!).
Finally, clean up those temp files once in a while. All kinds of 'things' can be lurking in there and ...set your browser to 'recheck the page' not auto-check.
Hope this helps!
Update (May 10) : Firefox 3.0 Release Candidate 1 should be available publicly available sometime this month according to this post to Mozilla Developer News. Closer is better :)