Firefox is quite a universal application (no pun intended). With limited exceptions, it can be run on Windows or OSX, regardless of Intel or Power PC processors. However, Firefox for OSX can also be optimized for each specific type of processor, greatly improving speed and reliability.These builds also can add Aqua form widgets to Firefox, making forms show up in OSX-style instead of how they show up regularly.
Now that Firefox 2.0 has been released, here are the optimized builds for Power PC and Intel Macs, courtesy of Beatnik Pad. The optimized versions are provided under the name Bon Echo, since the Firefox name (and icon) cannot be used for non-Mozilla releases.
G4-optimized Firefox 2.0
G5-optimized Firefox 2.0
Intel Mac-optimized Firefox 2.0
Thanks again to Beatnik Pad for these! Note: If you have any problems with certain web pages not recognizing your browser as Firefox, be sure and check out this page (its a simple fix). Enjoy!