Edit: Fixed code. Now works on quadstreams.

Edit 2: Berylium has a better solution. Look in the comments.

So, about an hour ago, I heard of an incident where two of my friends were doing a multi-stream and one of the viewers was upset on having to view both streams. They complained that it made the stream they wanted to watch too small, and caused performance issues and that they would prefer if the other streamer just wasn't there. I wasn't there at the time, but from what I was told, people were blunt, there was unnecessary tension, and all in all everyone was butt hurt by the whole incident.

So instead of being angry, I have a nice simple solution. I wrote a small bookmarklet that will strip out all but the first stream from a multi-stream session so that if you only want to watch one stream, you only need to. To use, create a new bookmark and copy the code below into the URL field of the bookmark. Then when you want to strip off the other streams, just click the bookmark:

javascript:(function(){var p=document.getElementsByClassName("flexPlayerOuter");var c=document.querySelectorAll(".flexPlayerInner");for(var i=1;i<p.length;i++){p[i].parentNode.removeChild(p[i]);}var s=c[0];s.classList.remove("flexPlayerInner");s.classList.add("flexPlayerInnerFull");for(var i=1;i<c.length;i++){c[i].parentNode.removeChild(c[i]);}})();

Let me know if this helps you or if you have any issues.