Well, I broke my FIrefox install big time. I added a bunch of extensions and restarted FIrefox, now I get no window. firefox.exe shows up in the processes, but not in the applications window of the Task Manager.
Off to the Firefox Support Forum, unless someone here knows how to fix it. I uninstalled, deleted and reinstalled, but no joy...

PS I like Thunderbird, and I sure was liking Firefox tillI broke it badly...