Well, new versions of Firefox do not support the PowerPC processor. You could consider a separate project that repackages Firefox code for PowerPC. It's called: TenFourFox.

Thank you, Sir. Your answer helps. Disappointed by believing in the FF website, and the general abandonment of so many viable Mac's... I did backup my bookmarks to my desktop but it's a .json file I don"t know how to access. Any ideas on restoring my bookmarks?