Rated 5 out of 5 stars
Folks, did you notice since Firefox 42 was released that every time when you open a full screen Youtube video, the same annoying message appears. It says to press escape to exit full screen. Yes, there was an about:config entry that allowed deleting this message but Firefox 42 changed something and that no longer works.
This extension nicely eliminates that message. To the developer, thank you so much.