Did not find it useful after using it for over a week. A few times it got accidentally clicked, but the most annoying thing that made me remove this, is the fact you cant scroll after you enable this mode. So I would suggest you update this, and I'll try it again, and consider changing review.

As mentioned in a previous review, if the video is pillarboxed (rather than letterboxed) the youtube masthead cuts of the top of the video.
This doesn't tend to be such an issue in a resizable window but is always the case in a maximized tab on a 16:9 screen which is the way I tend to use this.

It would also be nice if the progress bar and controls scaled with the window, although that is not a deal breaker like the above.

Sorry to raid on the five star parade, but I am fully willing to change this review to 5 if this problem gets solved:

It cuts the top part of the video off, I assume because it wants to fill width and disregards available height.