Hi Ellie111, boot the computer in [http://windows.microsoft.com/en-hk/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows Safe mode with network support] (press F8 on the boot screen) and then see if that helps. Most often issues like that are caused by a firewall or/and security software which doesn't recognize new Firefox (and for that blocks the new firefox version). You have to remove all program rules for firefox from your firewall and let it detect the new version of the browser again.{In windows safe mode with networking, security software is disable} thank you