CC is retired and is into YouTube videos now, but lately he's getting notifications to watch videos on HTML5. How can he watch those? Leo says that any browser can stream HTML5. YouTube has converted all videos to HTML5 now. If he right clicks on the video, it'll give him information on what kind of video is playing.
The chatroom says that CC could have installed a player as its default player and that's causing the confusion. CC should look in his browser menu and go to add-ons. If he finds one there, he should disable it.