Unable to connect from Firefox to anything despite complete removal and reinstall

Other browsers work fine - Edge, Chrome. Firefox had been working fine and abruptly started behaving badly. I powered down my system and restarted, that's when the "Unable to connect" started. Uninstalled and reinstalled, still happening. Uninstalled and scrubbed system of all relevant traces of Firefox (didn't meddle with minor registry entries), restarted and reinstalled. Still "Unable to connect". I have exhausted my knowledge set and the only thing I know of that I have yet to try is monitor the ethernet stack or process activity. Help!