The new draft spec of WebGL changes the name we use to get the context from the canvas; it used to be
moz-webgl for Mozilla or
webkit-3d for WebKit. The new standard is
experimental-webgl, which the current nightly builds of Firefox seem to use (though they also seem to support the old name), but the current Chrome doesn’t; it still uses
webkit-3d. I’ve not had a chance to check with Safari. [UPDATE] in the comments, murphy tells us that it works in the latest WebKit/Safari.
Anyway, it looks like the best bet for the time being is to support all three, so I’ve updated the lessons and the WebGL Cookbook recipe to do that; once Chrome’s moved over then we can switch to just using the new name.