Youtube error on "Save to watch later" or "Save to playlist" with infinite loading

Firefox Development
#1

Hello all.I have a problem since Firefox is updated to last version.When I visit Youtube,I can’t save videos to watch later or in playlist and I also got infinite loading when I scroll page to the bottom.
Upon clicking on save to watch later I got the option to login (even if I’m already logged on) and after that I got this error:

  1. That’s an error.

The request method GET is inappropriate for the URL /youtubei/v1/browse/edit_playlist. That’s all we know.

This error is not present in chrome or any other browser.

#2

hi i am getting this error as well if i go to youtube sometimes it signs me in and others it does not this happen when on new firefox version and i cant subscribe as even if i am logged it it tell me i am not signed in

#3

yes it’s anoying, it’s making me think of changing mozilla as primary browser