Mozilla is planning to release beta 8 sometime next week and so are we. I pulled source from mozilla-central tonight and made the small bustage fixes needed to continue compilation, and this post is being made from beta 8 in debug mode as we speak. There are still a number of blockers that Mozilla must resolve, but I expect that many of them will be deferred to beta 9, especially the Mozilla Sync-related issues. Most of the critical API and stability fixes are in, though, and they look good.
So far in Firefox beta 8 performance continues to get better, there are some interface improvements, and a number of the glitches in the renderer are gone. On our side of the bug fence, update notification appears to work and all of the known crash bugs are stamped out. We're also planning to deploy a G4/7400 version at the request of those users, and I have a few ideas for a G5-specific version. A G5-specific release was always planned, but the Mozilla source is terribly unstable even with -mcpu=G5, let alone -fast, and I couldn't sort this out in time for beta 7. However, I may be able to use ISA-independent tuning parameters to squeeze more oomph out of it, which is useful to me personally typing here on this quad G5. No promises yet but I am planning to do some tests this weekend to see if such a build will be stable.
One noticeable problem which comes late in the game is that unaccelerated graphics performance, which 10.4Fx is intentionally limited to, is slower in Firefox 4 due to a performance regression in the Cairo backend. We really need this, and Mozilla has marked it blocking final as it affects all platforms. The problem is most acute with animated images; you can track this bug yourself in Bugzilla. Hopefully it gets fixed sooner than later. We're monitoring it.
10.4Fx beta 8 also introduces our own infrastructure and livery, just like Classilla. You'll like it.
Watch this space!