WebGL provides a close match to OpenGL for incorporating 3D into Processing.js, but it does present some issues when trying to port over code. There are interface differences, changes to the interface are common, and some functionality isn't available at all such as point smoothing.
==Browser Unification==
One important feature provided by Processing.js is that it hides the differences between browsers. Web standards are often loosely defined, and thus variations can exist. These variations not only exist between different browser vendors but can even exist between versions of the same browser on different platforms. Something as simple as key events can vary widely between browsers. Processing.js hides all these intricacies from the user keeping it simple for content creators.
==Conclusion==