Beta 9 is now available (changesets coming, hang tight). Mozilla is doing more work on the graphics and layers code, which is visible in a couple sites that for me have broken (and I will be filing reports), but also in that overall drawing performance is in general better. This is important because 10.4Fx does not support hardware acceleration, so anything that gives us a win in software is precious.
Other things in beta 9 include a less flickery title bar (hopefully), which was a very annoying thing that cropped up in beta 8. Although it was an infrequent irritation on my G5, some users got really walloped by it. Mozilla fixed some part of this for Leopard, but that fix doesn't help Tiger, so 10.4Fx b9 has a separate rendering path for 10.4 that uses a naughty kludge. Because of this, the title bar does look ever so slightly different in 10.4 than 10.5, but only if you're looking for it. The title bar still does not always match the window gradient, but this is part Mozilla's bug and part ours. If you are really anal about that, install a Persona; they always work.
The UI was also adjusted to bring the app to the front when a window is clicked on. I am dithering over forcing the window up, or just forcing the app up, so that you can type but keep your window ordering -- I'm leaning towards the second, but will take arguments for the first. You can always click the Dock icon to bring the whole application and all windows forward, and this fixes the bug in beta 8 where sometimes it didn't bring anything forward when you clicked on a background window. It uses Carbon, don't tell Steve! Oh, and find Sluggo! We miss Power Computing! Classilla users will have seen an earlier version of this easter egg before. No fair reading the changesets to find the magic words.
Note that Flashblock as of this writing is not yet upgraded for beta 9, which should be a oneline change for them. If you really need it (and most of us do prefer it), you might want to wait until it is, or use an equivalent.