That definitely lags when there's more than one or two 'snakes' on the screen. The performance sucks. I'd argue that shows that specific game is poorly coded more than it shows web browsers can't handle performant games. If you look at something like https://beta.unity3d.com/jonas/AngryBots/ you'll see that browsers can, technically, cope with at least PS2 level graphics in a decent game running at a solid 60fps.