And that would be great. A more up-to-date gcc MPW tool would be a fabulous start. You might even be able to bootstrap it with the existing gcc MPW tool. If you can get up to and over gcc 4, fat city, dude. But even gcc 3.x would be better than nothing and would compile relatively late Firefoxen (at least Mozilla 1.8 level, maybe even 1.9.0). The problem there is writing a widget library for OS 9, and the build system, but those are partially solved problems.
This is one serious advantage the Amiga community has: they have a maintained toolchain. We don't. CodeWarrior, mercifully, was far ahead of its competitors, so it remains still pretty functional.
This is not clear, but my guess is it will not build on PPC. Camino 3 -- and I note for the record there is no guarantee Camino will live that long, but I digress -- will jump to WebKit and WebKit2 should be in full swing by then. It is questionable that WebKit2 will build as is on 10.5 by that time, and I guarantee it won't build on 10.4 (it probably has dependencies on the posix_spawn family of functions to implement its split process model; they don't exist in 10.4 and we code around them right now in TenFourFox). WebKit is reasonably system-independent, but most of the features that Camino will require will probably need 10.6 at a minimum. I can't really fault them for not wanting to continue to support 10.5.
Some of the PPC stuff is being accepted back, but I'm only submitting the POWER-generic code and not the Power Mac specific optimizations because Mozilla really doesn't want to be supporting Power Macs even with TenFourFox being a well-regarded port. While in fairness most folks at Mozilla are sympathetic to supporting PPC in the cross-platform portions of code (JavaScript, layout, etc.), their OS X-specific widget and gfx maintainers aren't (the guilty know who they are). In fact, TenFourFox 8 probably uses less than half of the official Firefox code in its widget library after all the rewriting I've been doing over the last week and I'm likely just going to spin off widget/src/cocoa/ and */themes/pinstripe into widget/src/tiger and */themes/tigerstripe instead of dealing with all the post-10.4 crap they're loading them with (CoreUI, NSTrackingArea, etc.).