As far as I'm aware, browsers have been making use of any available GPU acceleration for rendering 2d contexts since 2012[1]? The example supplied by Google[2] (on the first link) definitely requests a 2d context for the canvas.

[1] - https://developers.google.com/web/updates/2012/07/Taking-adv... [2] - http://fhtr.org/gravityring/sprites.html