cc and XP OS and FF cache

I just installed CC on my XP OS where I use FF 3.0 as my browser. When I run the cleaner it asks me to close the FF browser, but, it's not open. When I run the cleaner it says it has skipped cleaning the FF cache, however, when I run CC again it then cleans the FF cache. I'm confused. Can anybody help?

Press CTRL+ALT+DEL on your keyboard and look for a running Firefox.exe process, if it's running even hidden in the background that's why CC won't clean it.

In some instances it may take Firefox some time to fully close down even after the GUI disappears off screen, and it could be because of a Firefox add-on you're using.