You need to wait until the plugin releases its' "grip" on Mozilla. If can't wait, ending the processes using Task Manager should do it.
No, it doesn't mean someone access your computer remotely. You should report it to Mozilla.org forums so they can check the issue. This happened with Firefox too but was fixed with v1.5
Using Mozilla 1.7.12, win XP home, sp2.
Just tried to use CCleaner and it told me to first SHUT down Mozilla.
I had closed it, Mozilla was closed out as far as I could tell. Nothing was showing on my screen to indicate Mozilla was in use.
Did Ctrl-Alt-Del and TaskManager/Processes, showed that MOZILLA was in use.
Clicked END PROCESS and it went away.
Why/HOW could Mozilla be active and not show on my screen somewhere?
Does that mean someone accessed my computer remotely?
Thanks
Ben

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic