In order to see this at 60 fps, you have to watch it in something like Chrome. For whatever reason other browsers can't or aren't supporting it. I heard Safari can... but I have no experience with it. And this of course is considering your computer is fast enough to stream this online. I even experienced lag watching this video online at 720p, 60 fps on Chrome.
I notice I'm able to watch this and other 60 fps videos offline, without any, or next to no delays. So downloading is always a good option guys.