I followed the advice in this answer and entered https://youtube.com/tv in my FireFox browser. A login screen appeared which I could skip and indeed, all videos appeared in a large full screen format.
But now everytime I go to Youtube I get that format!
(Even in some continue where you left off state).
How do I get my previous 'browser' Youtube interface back?
Best Answer
Signing out from Youtube (Google) and then signing back in seemed to do the trick.