Enable YouTube HTML5 fullscreen for embed/iframe

javascript:(
    function ytfs()
    {
      var objI = document.getElementsByTagName('IFRAME');
      var n = objI.length; for(var i=0;i<n;i++)
      {
        if (objI[i].src.indexOf('youtu.be') > -1 || objI[i].src.indexOf('youtube.com') > -1){
          objI[i].setAttribute('allowFullScreen', '');
          objI[i].src = objI[i].src;
        }
      }
    }
)();