Firefox now requires acknowledging Flash EVERY time
As of Firefox 69, you must now acknowledge and activate Flash EVERY time you use it. It will no longer allow you to 'remember' for a website.
Oddly, I did a test with the Xfinity Stream website, and did not get a popup, and it works. There is an icon to allow/disable in the address bar, so maybe Comcast is recognizing it's blocked and switching to HTML5?