Problem with Xfinity online TV: caused by flash?

When using Win 8 PC and IE 11.0.96 to watch live TV on xfinity web site while connected to the TV via HDMI cable, things seem to work okay, UNLESS I unplug the HDMI cable, or hit the back button to see the TV schedule, or even just turn off the TV without touching the computer (along with other actions).  If this is done, then when the image is restored, it will be frozen.  No amount of waiting or reloading will bring the streaming back.  The only fix seems to be to log out, close the browser, and then log back in.  I have flash 23.0.0.162

I suspect the PC's video software or flash.

I had been using firefox, but watching xfinity videos with firefox drives the PC into CPU overdrive, as evidenced by constant running of the fan at high speed.  Switching to IE mostly fixed that.

Note that this is not the same problem with intermittent freezes and pixelating that many people have which is more of a buffering thing.  This just freezes stuck and stays stuck, like someone hit pause.

Suggestions are appreciated.

Thanks.