This is mostly a Javascript/Canvas question and not a Construct 2 question. Perhaps this is best directed towards the C2 developers since they have built an option to enable or disable WebGL in C2 if the browser supports it.
I've made a few HTML5/JS demos using canvas before, but I have never enabled WebGL acceleration for them to speed them up. Could someone who is knowledgeable on this explain how WebGL can be enabled for your canvas-based app if the browser supports it? Is there a library (like modernizr, which detects for canvas capabilities) that simply allows you to 'turn on' WebGL acceleration if the browser is capable?