Since 40.0 update, switching to full-screen video became sluggish and ugly, because it leaves behind the whole top bar (like with F11) for a second.
Subject.
Since today's 40.0 update, with Youtube videos, full-screen acts like Firefox is switching to full-screen mode - showing the full-screen video fit under the top bar - for half a second. Full-screen Flash/HTML5 video has nothing to do with full-screen mode for Firefox and AFAIK it never had. Why did it change? It does not hamper base functionality, but is a little annoying and it seems pointless, like a bug or an error.
Wšě wotmołwy (1)
pic related (didn't attach to the question itself)