Greasy Fork is available in English.
Adds the likes/dislikes light-saber to YouTube thumbnails, so you can avoid watching crap videos. Activates when mouse passes over a thumbnail.
< YouTube Thumb Likes Dislikesについてのフィードバック
Sorry I didn't see this message until recently. I believe the problems were fixed anyway.
Not working (as of 12th/November/2015)
It's not showing any ratings when I hover over a thumbnail