A lot of current WebGL code has code to handle old compatibility problems between the browsers; in particular, I always check for the old context names (webkit-3d/moz-webgl), the CanvasFloatArray/WebGLFloatArray move, and the move from getShaderi to getShaderParameter.
It looks like these checks might now be unnecessary; checking Firefox and the Chrome dev channel, it looks like both of them use the current spec for all three of these. In general, Safari seems to be ahead of the others when it comes to spec compliance, so it’s probably sorted too…
However, I’ve only checked on a PC, and it would be really interesting to hear what everyone else sees – in particular people using Macs and Linux. I’ve put together a page that checks browsers for the three changes above; test results would be much appreciated!
Here’s the link: http://learningwebgl.com/tests/cruftcheck20100104.html