Firefox problem

[Phil]

Thank you for reading this tale of woe.

I reinstalled Kubuntu after a data loss disaster and now I have this 
Firefox problem. The error message reads:

"Firefox is already running, but is not responding. To open a new 
window, you must first close the existing Firefox process, or restart 
your system."

Firefox is not actually running but something in the system thinks that 
it is. Restarting the system does not help.

It is very likely that I've created this problem after restoring the 
backup. I think I had Firefox running during the restore process.

Can anyone offer any suggestions?

-- 
Regards,
Phil