After downloading an update, firefox says "your computer must be restarted to complete a previous upgrade of firefox. do you want to reboot now" and will not start.

Firefox will not start, or allow windows xp to uninstall the program. When I attempt to start the program, firefox says "your computer must be restarted to complete a previous upgrade of firefox. do you want to reboot now? It gives the same message after rebooting, and will not start, or uninstall. I also downloaded it again, same thing. 

Firefox will not start, or allow windows xp to uninstall the program. When I attempt to start the program, firefox says "your computer must be restarted to complete a previous upgrade of firefox. do you want to reboot now? It gives the same message after rebooting, and will not start, or uninstall. I also downloaded it again, same thing. == This happened == Every time Firefox opened == I downloaded an update.