WebKit/Blink currently dispatches fullscreen events to elements, which makes sense, and matches our initial proposal of Fullscreen API . It was not implemented that way probably because the current Gecko approach is easier to implement. The spec has been changed to dispatch those events to element, and fallback to document in cases at whatwg/fullscreen#90.  https://wiki.mozilla.org/Gecko:FullScreenAPI#fullscreenchange_event
This is indeed something we want to do before we unprefix fullscreen.