Official build is not optimized for Mac OS, that's why community builds exists. And since you can't use official brand so most of the builds stay in codename which Minefield is Firefox 3.0.
Here you go:

1. Neil Lee, BeatnikPad build
   Platform: Intel, G5, G4
   I think his is my favor build for Mac, much smooth and speed than others.
2. elfurbe's Nightly Builds
   Platform: Intel, G5, G4, G3
   It's nightly builds and most updated, if you are hungry.
   

There are some community builds from Japan, but they always keep the official brand for their builds, it's illegal, so i just passed.