Mozilla shipped Firefox 3 RC1 recently. I don't see any major changes beyond them moving the "default browser" check to the install wizard and, of course, most of my Firefox add-ons no longer work. (I assume that's just temporary.) Anyway, here are the release notes, which provide no valuable information at all:
Firefox 3 (Release Candidate) Release Notes
Released: May 16, 2008
This Firefox 3 Release Candidate is a preview release of Mozilla's next generation Firefox browser and is being made available for testing purposes only.
Preview releases are published to collect feedback from Web developers and our testing community before advancing to the next stage in the release process. The final version of Firefox 3 will be released when we qualify the product as fully ready for our users. Users of the latest released version of Firefox should not expect all of their add-ons to work properly with this preview release.
It's interesting to me that they're referring to this release as a "Firefox 3 Sneak Peak" on the main Mozilla site now. Presumably, that's so the normies don't get freaked out by a pre-release version.
Download Firefox 3 RC1 (And not to be totally Anglo-centric, but that list of language versions is ridiculous. How about detecting the language of the browser currently being used and put that as the suggested download at the top? Just a thought.)
Update: According to this review (on a site that has apparently brazenly stolen the style sheet from the New York Times Web site, by the way), there are some new features in RC1, including performance improvements, memory use improvements, Places improvements (this feature isn't actually called "Places" in the UI anywhere that I can see, for whatever that's worth), Location Bar auto-complete improvements, and some visual changes (though it looks the same to me, compared to Beta 5).