After closing firefox browser and then going back to open a shortwhile later the browser won't open. A a message appears saying firefox is running and to close it down first. I check with taskmanager and it shows it is not open and I have checked with my firewall and that shows it is not running. I then go into services via taskmanager and completely shut firefox 32 exe. Once this is done firefox begins to work as normal. I have experienced this problem a few times now and occurs intermittently. My computer runs on windows 7 64bit. Firefox is the latest version.