You can get Firefox 3.6.16 from http://www.mozilla.com/en-US/firefox/all-older.html

There is a third party version of Firefox 4 that runs on OS X 10.4/10.5 and PPC Macs, for details see http://www.floodgap.com/software/tenfourfox

Thanks a million!

TonyE, I'd like to add my thanks for this "life-saving" solution. It's not like Mozilla Firefox to create such a download firestorm. Following my failure to apply Firefox 4.0 ("wrong architecture"?), until I picked up your suggestion I wasn't able to locate a download so that I could revert to the earlier version of Firefox.

Use Tony's suggestion. I am running it right now and it is awesome. I love Mozilla but they basically screwed all of those older Macs over. Come on Mozilla. These Macs still work, and there are plenty of people with them out there.

I just returned from the Apple Genius bar, where you can bring in any Mac for 20 minutes worth of trouble-shooting and help. The tech told me that the latest upgrade of Firefox is only for intel-based Macs. I wish they would have warned me clearly when they "invited" me to upgrade. He helped by going to Firefox and finding the 3.6 version, which I then downloaded. I then threw the Firefox 4 icon in the trash. Since it had never "opened", it didn't leave any other files to look for in the library, etc.

All my bookmarks and preferences were there when I opened Firefox 3.6, as they were stored on my computer in preferences.

Good luck to all!

Thanks for the help!!! It's much appreciated ... I just returned from the Apple Genius bar, where you can bring in any Mac for 20 minutes worth of trouble-shooting and help. The tech told me that the latest upgrade of Firefox is only for intel-based Macs. I wish they would have warned me clearly when they "invited" me to upgrade. He helped by going to Firefox and finding the 3.6 version, which I then downloaded. I then threw the Firefox 4 icon in the trash. Since it had never "opened", it didn't leave any other files to look for in the library, etc.

All my bookmarks and preferences were there when I opened Firefox 3.6, as they were stored on my computer in preferences.

Good luck to all!

While I understand that the PowerPC architecture can't be supported forever it would have been nice if when I opened Firefox 3.6.16 I didn't get a window suggesting I upgrade to 4.0 without telling me along the way that it won't work on PPC. I had to find 3.6.16 and install it again. Thanks to TonyE for providing the link.

Firefox developers: please put a PPC disclaimer on the 4.0 download page and put a link to 3.6.16 somewhere so PPC owners who mistakenly download 4.0 can re-install it. Thanks.

Mozilla are working to prevent Mac users with non-compatible systems from getting the notification about Firefox 4, and also not displaying the "Download Firefox 4" button on http://www.mozilla.com

Don't worry buddies, there is a fork of Firefox 4 for PowerPC Macs, TenFourFox . Not all is lost, there are people out there that believe that PowerPC architecture still rocks :).