When it works, it works flawlessly. However, sometimes, for no apparent reason, it just stops working for a few hours. Unfortunate, but not necessarily within the developer's control.
Thanks for reporting this. I just released an update to address the recent issues, but the extension now requires users to enter a personal YouTube Data API key. Instructions for setting up a free YouTube Data API key, and an explanation for why this is required, can be found here: https://github.com/elliotwaite/thumbnail-rating-bar-for-youtube
