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 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

If there are problems with updating or with the permissions then easiest is to download the full version and trash the currently installed version to do a clean install of the new version.

Download a new copy of the Firefox program and save the disk image (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

Thank you very much for the info. Have installed Tenfourfox and add-ons but still cannot view video content. Any suggestions? Keeps indicating I need flashplayer. Thanks.

How-To Guide: How to enable Flash on TenFourFox 6 and 7

• http://forums.macrumors.com/showthread.php?t=1226744
• http://lowendmac.com/ed/royal/11sr/tenfourfox-flash-and-ppc.html

Thanks cor-el. I went to the first link you suggested and followed the instructions by going to "about:config" and changing the value to true on flashplayer but still cannot view videos. I am running flashplayer 9 which I think is the latest version I can run on a Mac G4 Power Pc with no intel? Installed all add-ons I could think of that may resolve the issue but still to no avail. My current system is Leopard 10.5.8. Any further suggestions? Thanks