Can not log in to Youtube
YouTube login is completely broken in FireFox only. I am logged in to my google account and that seems to work fine. Youtube however is messed up. When I visit the page directly it shows my account picture in the top right (see image 2) and it suggests videos correctly and even continue watching looks right. However, I can not comment, post videos, view history, or even reload the page(f5). Doing so brings up the "sign in" button. clicking the button and entering my google username and password gives the error (image 1).
Things I've done: 1) cleared all cache, and saved logins, and data. 2) "refreshed firefox" 3) uninstalled firefox, deleted %appdata%\mozilla\firefox\profiles\, rebooted and re-installed firefox.
I have a gut feeling this is something wrong that keeps being re-introduced with sync. Although youtube works fine on my other PC and my mobile devices. so I'm not sure what.
Is there a full uninstall? (including registry and left over files)
Youtube works fine in chrome and Edge so I'm sure it'd firefox and not any other network problem.