This add-on contains lots of bugs. First; it extends the lenght of player so if video is 16:9 it becomes much more long in player base and i have black bars on top and bottom of the video. My YT home page and YouTube users' profile pages also broken because of this add-on. They solved lots of bugs so i am just turning it off for now, i wish they can solve new issues without any more time.
Edit: "Limit Page Width" solved the bug which i mentioned (video width and home, profile pages). Thanks. But changing thumbnail quality breaks thumbnails to gray boxes.