Greasy Fork is available in English.
Hover a thumbnail on youtube.com and click an icon at the right: "Not interested" and "Don't recommend channel"
< Feedback on YT: not interested in one click
The new 1.1.6 should fix it. I guess you were using the inline preview player, which I always disable in account prefs.
Apparently, as of today, it's working normally. Maybe reinstalling did it, maybe something broke on the Youtube side and interfered.
Also, awkwardly I received the notification of the replies in the spam box when it should have been in the inbox, that's why I didn't reply ASAP.
Stopped working entirely.