Firefox 4 versions and later '''do not run on a PowerPC Mac'''(like yours) and require at least OS X 10.5 '''and an Intel Mac'''. see: [http://www.mozilla.org/en-US/firefox/11.0/system-requirements/ Firefox 11.0 System Requirements] The latest supported version for your ppc mac is '''3.6.28''' you can download from here: http://www.mozilla.org/en-US/firefox/all-older.html [http://www.mozilla.org/en-US/firefox/3.6.28/system-requirements/ Firefox 3.6.28 System Requirements] 1. Download a new copy of the Firefox program(3.6.28) from the above link 2. Trash the current Firefox application to do a clean (re-)install. 3. Install the new version that you have downloaded(3.6.28). Your profile data is stored elsewhere in the [http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox Profile Folder], so you won't lose your bookmarks or other personal data. see also: [https://support.mozilla.org/en-US/kb/Installing%20Firefox%20on%20Mac Installing Firefox on Mac] [For older Macs that aren't supported in Firefox 4+ versions, if you like, try TenFourFox for PowerPC's running Mac 10.4.11 & 10.5.8] http://www.floodgap.com/software/tenfourfox/ http://tenfourfox.blogspot.com/ https://code.google.com/p/tenfourfox/wiki/PluginsNoLongerSupported thank you Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

Thanks so very much! I was afraid that I'd never figure out which old version of Firefox it was that still worked so well for me. Sadly, Apple abandoned this architecture all too quickly and relegated those of us who had fairly new computers to using what was available at that time. Much appreciated!