This is a great idea, but I have to rate it 3 out of 5 stars.

For one, the videos I flag have shown up on my recommended again. I realize this may be due to the fact that I am not logged in to YouTube and I clear my cookies once I am done browsing. However, considering that other add-ons keep my settings in spite of that fact, it is annoying at best and triggering at worst. I am willing to give Mozilla the benefit of the doubt, however, especially since this add-on is quite new.

So that is one star taken off. The other star is taken off because there is no way of blacklisting entire channels. Given that many channels provide relatively the same amount of content, that is a very strange feature to leave out. There are many channels who effectively show up on everyone's recommendations no matter what content you watch on YouTube that not everyone would like to see. I am only taking off one star for this because, again, this is a new add-on, and I know Mozilla is always open for feedback, and I don't want to drag down the rating too much. Still, I can't help but feel as though this feature is intuitive for the add-ons purpose, thus it is a necessary one.