My Wife's computer - still on Windows 10 - says it can't start Firefox as it is still running, hitting the "close Firefox now" button just returns us to the same screen. I tried to uninstall and reinstall Firefox it tried to do a "reinstall" it says her profile is no longer available, while inconvenient she still should be able to start it up, but it still gives me the same message. that it is still running and needs closed. Trying to "close it doesn't do anything. I have restarted several times and even did a shut down and restart. Nothing seems to work. I assume some "stub" of Firefox is out there in the system/cache making Firefox think it is is still active but I can't find it to shut it down. Where do I need to go to "end task" on this phantom Firefox?

Other information: 1. We have Norton Security software installed, if that matters. 2. The same seems to happening to Thunderbird, but maybe I need to go to another help forum for that? 3. I am entering this issue from my computer that seems to be just fine with Firefox, so can't send browser data as it is irrelevant to the issue (it's on a different computer and install instance.