When I shut firefox down and subsequently try to restart it, an error message pops up telling me it is already running and I have to restart my system. I am unable to get firefox to start up again until I reboot my system. Once reboot is complete it starts up fine, until I shut it down again. I then have to reboot again to get firefox up and running again. I have tried just waiting and trying several minutes to hours later to restart firefox, but the same error message comes up until I reboot the system.