Updating the firmware appears to be the reason the IE plugin worked THIS TIME. It never worked for this cam before, and so I incorrectly assumed It would not work again... Now I’m supicious that using other browser(s) played a role in this camera’s instability.
It’s frustrating to deal with browser plug-ins that work for one camera, and don‘t for another.
Lesson learned - just because the browser opens the camera, doesn’t mean everything’s working under the hood.