Current browsers consider flash-content 'unsafe', the youtube-embedded videos are such.
To view them regardless .. click on the shield-icon in your adress bar (see attachment), and you'll get an option to 'load unsafe scripts on this site'. When you click on it all embedded youtube videos are displayed.
Unfortunately I haven't found an option yet that permanently displays all unsafe scripts on TUS, so you'll have to use this every time
Maybe it's for the best..
Anyway, here's a video to test: