"youtube.com is now fullscreen. Exit fullscreen (Esc)"

 full-screen-api.approval-required to false
 full-screen-api.transition-duration.enter to 0 
 and full-screen-api.transition-duration.leave to 0

When I switch YouTube video to fullscreen, this message pops up: "youtube.com is now fullscreen. Exit fullscreen (Esc)" after having seen this evil message ten thousand times, I think I understand that I can exit with Esc, and I don't need to be reminded again. How can I disable this evil feature on Firefox 45 ? I have tried setting full-screen-api.approval-required to false full-screen-api.transition-duration.enter to 0 and full-screen-api.transition-duration.leave to 0 none of these help.