Xfinity is actively blocking streaming in Firefox.

https://www.xfinity.com/stream/ • (Windows 10 desktop PC)

It hangs forever at the purple xfinity stream ... page.

xfinity stream was working previously in Firefox for years.

xfinity stream works fine in Microsoft Edge, in the Xfinity stream app on my Android cell phone, and through my Roku Ultra.
Netflix and HBO MAX and YouTube videos play just fine in my Firefox browser.