The last version that works with PowerPC processors is the 3.6 branch. You can download from http://www.mozilla.org/en-US/firefox/all-older.html

Thanks for the info on the applicable version of firefox. Just curious as to where you found the answer. I never found it after spending some time on the Mozilla web pages.

It was in the release notes for version 4 IIRC

See:

• http://www.mozilla.com/firefox/7.0/system-requirements/
• http://www.mozilla.com/firefox/3.6/system-requirements/

For an unofficial Firefox 7 compatible version (TenFourFox) that runs on PowerPC Macs with OS X 10.4.11 or OS X 10.5.8 you can look at:

• http://www.floodgap.com/software/tenfourfox/
• http://www.macupdate.com/app/mac/37761/tenfourfox