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.
>Practically any page with a non-trivial shader freezes Firefox for up to a minute or sometimes even more on my machine.
That makes me glad I disabled it.
[1]: In about:config, I set webgl.disabled to true.