For anyone who suffers from terribly long load times/freezing when compiling the shader, this is caused by the ANGLE wrapper Firefox and Chrome use to convert the WebGL calls to Direct3D 9. You can get better results by disabling it: http://www.geeks3d.com/20130611/webgl-how-to-enable-native-o...
I think the rationale for using ANGLE is to avoid driver bugs, but in my experience, it causes much more damage than the problems it solves. Practically any page with a non-trivial shader freezes Firefox for up to a minute or sometimes even more on my machine.
I just checked http://www.browserleaks.com/webgl on Win 7, and Firefox 30's ANGLE uses Direct3D 9, whereas Chrome's Canary (v38, best performance) uses Angle with Direct3D 11.
Firefox might upgrade this sometime, but Aurora (Firefox 32) still uses Direct3D 9.
My understanding was that ANGLE was done so that DX9, 10, 11 could be used underneath for rendering while doing OpenGL -> DX translation, main reason being unstable GL drivers.
Nowadays, NVIDIA provides GLES2/3 apis, but not sure about AMD/Intel.
You should check whether your drivers and browsers are uptodate. Most WebGL pages work just fine these days, although some (e.g. many shadertoy shaders) tend to use too expensive shaders which might be slow on older integrated GPUs from Intel or generally mobile GPUs.
I think the rationale for using ANGLE is to avoid driver bugs, but in my experience, it causes much more damage than the problems it solves. Practically any page with a non-trivial shader freezes Firefox for up to a minute or sometimes even more on my machine.