Last I looked, the vector math part of 3D wasn't handled by webGL, this uses Three.js to handle that, and looks to be the main bottleneck. Until you can do matrix/vector math using hardware, webGL is pretty much useless.
Modern matrix libraries like glMatrix
https://github.com/toji/gl-matrix
use typed arrays effectively to do very fast matrix and vector math in JS. A modern JS engine can transform such code into something very efficient, more than fast enough to do things like even first person shooters.
[1] http://metaphysicaldeveloper.wordpress.com/2011/12/20/implem...
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=644389
[2] http://www.altdevblogaday.com/2012/06/18/bringing-simd-accel...