From the 'not far now' files:

I've been following the development of Firefox 3.1 -- now renamed Firefox 3.5 -- since the first alpha release in July of 2008. It has been a long road, the but the end is (nearly) in sight.

Firefox 3.5 is currently at its Beta 4 stage and a code freeze for the Release Candidate (RC1) is now set for May 20th. Mozilla developer Mike Beltzner noted in a mailing list posting that Mozilla is down to some 52 code-blockers (issues that should be resolved) at the present time.

With a freeze set for May 20th, builds and testing to follow, we could see a publicly available Firefox 3.5 RC1 in early June.

It's far too early to tell at this point (in my view) how many release candidates Firefox 3.5 will have.

If history on past releases is a good guide, we could be looking at two or three release candidates prior to Firefox 3.5 being finalized. Firefox 3 went through 18 months of development  including five alphas, five betas and three Release Candidates.

There is lots of new stuff in the Firefox 3.5 release including private browsing mode, faster JavaScript execution and some HTML 5 support among other new features. I've been using the Beta 4 release since it came out and it has been very stable (for me at least) in day to day usage.

The one issue though (as is often the case with early betas) is that not all of my Add-Ons (extensions) work with Firefox 3.5 (yet). That's more of an effort for the extension developers though and as the final release gets closer, I'd expect that most of the extension developers will get on board.