Normally you don't need to register or set up any accounts to install or update Firefox. Is it possible that you set up Firefox Sync, to synchronize settings between different computers/devices? If that isn't it, I'd be very wary of whatever it is you installed. You may want to run some supplemental scans. These two tools are highly regarded: Malwarebytes Anti-malware : http://www.malwarebytes.org/products/malwarebytes_free SUPERAntiSpyware : http://www.superantispyware.com/