Firefox error message, "FIrefox is already running but not responding"

I can't open FIrefox. When I try to open it I get the following error message. "Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window." I opened Task Manager and could not find any instance of Firefox or Mozilla running. I uninstalled Firefox and deleted all the files and folders having to do with Mozilla and Firefox. Then I reinstalled Firefox. I continue to get the same error message. I am running Windows 11 64bit on a Dell laptop. Any suggestions? Ray