• Firefox 4 versions and later do not run on a PowerPC Mac.
• Firefox 4 and later require at least OS X 10.5 and an Intel Mac.
• http://www.mozilla.com/firefox/6.0/system-requirements/

For an unofficial Firefox 4 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://code.google.com/p/tenfourfox/

Firefox 3.6.x (Mac OS X 10.4 and later) can be found here:

• http://www.mozilla.com/en-US/firefox/all-older.html

Thanks, but this reply didn't help me. I went to that site and downloaded the 3,6 but it still wouldn't come up. I think I need to uninstall 6 first and I don't know how to do that without losing all my bookmarks

Download a new copy of the Firefox program and save the DMG file to the desktop

• Firefox 3.6.x: http://www.mozilla.com/en-US/firefox/all-older.html

• Trash the current Firefox application to do a clean (re-)install
• Install the new version that you have downloaded

Your profile data is stored elsewhere in the Firefox Profile Folder, so you won't lose your bookmarks and other personal data.

• http://kb.mozillazine.org/Profile_folder_-_Firefox

Help > Troubleshooting Information > Profile Directory: Open Containing Folder

See also:

• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox