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 12.0.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

• https://support.mozilla.org/kb/Installing+Firefox+on+Mac
• http://kb.mozillazine.org/Installing_Firefox#Mac_OS_X

Hi there, thank you for your reply, but I had actually previously uninstalled firefox, there is no trace of the application on my laptop that I can find. So there must be another issue as none of the downloads seem to work? I can't even get the dmg file on my desktop,

thanks again!