Greasy Fork is available in English.
Instant video previews in popup player by hovering or clicking video thumbs. Video ratings and resolution data shown on the thumbs. Gets video information without using a YouTube API key, which can be banned or limited.
Works perfectly for me on Firefox 74 on Ubuntu on 28 March 2020
Ratings and Previews work fine. I don't know how you did it without an API key but it does work. (The ratings-bar addon on the official Firefox addons site is the only other ratings addon that works — and that needs you to get a Youtube API key before it works properly.)
I didn't want the video preview feature but it worked fine before I switched it off in the options.