I think you already known that latest firefox version 13.0.x don't work with xp sp1, needs sp2 and above.

Try Uninstall Firefox from your computer

then Download the latest version(with your safari) from :

http://www.mozilla.org/en-US/firefox/all.html

and Install the version that you have downloaded (13.0.1).

Do not select to remove your personal data, your profile data is stored elsewhere in the Firefox Profile Folder, so you won't lose your bookmarks or other personal data.

see also for info : Install Firefox on Windows

thank you

Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

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Cannot uninstall firefox from control panel when I try to remove it, I get the message, "Your computer needs to be restarted to complete a previous upgrade of firefox. Do you want to reboot now?"

The reboot does not work and I get this same message every time.

Back up and restore information in Firefox profiles then download Revo Uninstaller freeware from : http://download.cnet.com/Revo-Uninstaller/3000-2096_4-10687648.html and uninstall firefox with revo. Then install a new copy of firefox.

thank you

Many thanks, problem solved with your help. Cheers.