How can I go back from YouTube TV to ‘normal’ Youtube

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?