problem with audio in videoconferencing meetings.

When I join an online meeting with Zoom or other similar sites, I can get video feeds fine, but cannot hear audio, or input audio (So the meeting participants cannot hear anything I say.) I'm using Firefox updated to latest version, on Windows 7 Pro.The Firefox WebRTC plug-in is always activated, so that isn't the problem. Speakers and headphones work fine on other sites, so it may be site-specific? I can't find any settings in Control Panel that would seem to deactivate audio. I'm open to any other ideas that don't involve using Microsoft Edge, but would prefer to try Google Chrome only as a last resort if nothing else will work.

Suggestions from DU geniuses?