Just a couple days ago, on September 20, I notice that once I go to any YouTube video, the video controls after the video starts playing disappear. They only reappear after the video stops playing.
I have Windows 7 64bit, and Firefox 64bit. I have the latest version of Flash Player 27.
It seems to be fixed now. I just went over to YouTube as I have been these past days, and the issue I mentioned above has been resolved. Thank you to Adobe if you did something to fix this issue on your end.