This add-on appears to work by telling YouTube that none of its video formats / file types will play back in its HTML5 player. That **used** to trigger YouTube's Flash player to load. But, YouTube has **completely removed** its Flash player code from its site, so now, all this add-on will do is cause YouTube's HTML5 player to display a message that the browser doesn't recognize any of the video formats available.
So I'm unclear as to why this add-on is still getting updates... since there doesn't appear to be any way it can work?
Unless there is some user agent trick or some other trick I don't know about... but then, if there is, that should be built into the plugin, shouldn't it?