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/4.0/system-requirements/
• http://www.mozilla.com/firefox/5.0/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/

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

Firefox 4 and later require at least OS X 10.5 and an Intel Mac.

I am running OS X 10.6.8 on an Intel Mac. So why can't I upgrade?

Again, I am NOT running a PowerPC Mac. It is an Intel based Mac.

Still not getting why I am unable to update to the more recent version of FireFox.

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 11.0.x: http://www.mozilla.org/en-US/firefox/all.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 if you uninstall and (re)install Firefox.

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