Firefox does not start up after closing it out

[Durhamhs]

I have Kubuntu 13.04 Beta 2 and when I X out of Firefox it seems to close normally. However, after trying to restart Firefox a box appears stating that Firefox is already running - please either close it or restart the system. Is there a cure for this problem?

[Teunis]

So do you still see Firefox in the list of processes when you do Ctrl+Esc?
And when you restart Firefox after killing the process from this list does it happen again?
If this is reproducible you might have a problem.
My first hunch would be it's some plug-in that hangs.

[dmeyer]

I have Kubuntu 13.04 Beta 2 and when I X out of Firefox it seems to close normally. However, after trying to restart Firefox a box appears stating that Firefox is already running - please either close it or restart the system. Is there a cure for this problem?

Noticed this happen but very rarely. Just close the dialog and try launch Firefox again and it seems to fix the issue. Though checking the running procceses is fun to check.