As an almost-last resort, disable Gnash and Lightspark, and install YouTube All HTML5 (to install it, in Abrowser, go to the add-ons menu, go to Add, and below Search add-ons, type "youtube all html5").
As a real last resort, go to the page of the desired video and replace "watch?v=" with "embed/". However, for more convenience, when playing a playlist, in order to watch the specific video inside a playlist, replace "watch?v=" with "embed/" and remove "&list=anythingelse", just remember to go back to the playlist page in order to be able to click on the next desired video. Best regards, ADFENO. Have a nice day.