I've been trying to resolve this issue of video links from the "my.xfinity" homepage not playing on my MacBook using Safari for about two months and still tthe issue persists yet there doesn't seem to be a need to list this as a problem on the support page. I have gone through a number of proposed resolution from the forum discussions to no avail. My last attempt was to stop using Safari (MacOS Sierra version 10.12.3) and download Firefox to use instead. That worked for about three weeks and then the same thing happened on the homepage using Firefox, the "Today in Video" page begins loading and get locked up trying to load the video selection icons and won't play anything that I select.
By the way, I've already uninstalled Firefox because it was eating up my battery life.