Detected when using <video> inside these bootstrap classes - modal (fixed) > container > row > col-md-X (float). When switching the video to fullscreen it did not show well and the video itself was actually positioned below the visible area of the screen. I looked at the css - https://code.google.com/p/webkit-mirror/source/browse/Source/WebCore/css/fullscreen.css?name=master and although I didn't fully understand why it uses static positioning (rather than fixed) these rules seemed incomplete. My workaround was to add these custom css rules that fixed the display (though I'm no expert if it has other side-effects). It might be worth fixing somehow in the original webcore css. /* make ancestors show fullscreen and cancel float */ :-webkit-full-screen-ancestor:not(iframe) { float: none !important; margin: 0 !important; padding: 0 !important; width: 100% !important; height: 100% !important; } /* hide fullscreen siblings */ :-webkit-full-screen-ancestor > *:not(:-webkit-full-screen):not(:-webkit-full-screen-ancestor) { display: none !important; } Thanks, Guy