Xfinity Stream not working on MBP / Firefox

I got Flash's pop-up reminder to uninstall it, so I did. Now Xfinity Stream doesn't work.

I can load a show's page, but all the images are blank boxes with titles. When I try to stream a show, it says I am offline ( I am definitely online), keeps trying to stream, and then gives up. It looks a lot like the page looked when Flash wasn't enabled. I wonder if this is related to Flash's demise?

I am using a MacBook Pro, OS 10.13.6 High Sierra, Firefox 84.0.2
(and before anyone asks, Firefox is my preferred browser. I do not have Chrome installed and do not intend to do so.)