Cure for the only bug I've met in Firefox

Firefox is the best. But there is a chance that you'll meet it's only bug. Here's the cure. The only bug (click me)

You'll only need this if Firefox tells you that 'this profile is in use' and you can't launch Firefox. No problem. Just Ctrl/Alt/Del then delete the only Firefox program running in your task manager. Firefox will launch perfectly. It happens when some stupid site launches a hidden browser. Don't panic. It's nothing serious. It's happened to me a couple of times.