Is it possible to render OpenGL to a WebGL context?
This is a strange question, but is it possible to pass a WebGL context to a browser plugin and have the plugin draw to it as it would to an OpenGL ES 2.0 context?
I have heard this might be possible.
Depending on the browser (version) this might be possible through obscure, lowest level tinkering hacks; I don't recommend it.
But there's a way to use a WebGL canvas from a plugin: The WebGL context it part of the DOM, so it is perfectly possible to use the WebGL context through the DOM, and since plugins have full access to the DOM, a plugin can control the WebGL context. The same holds true for Java applets, which is a really nice thing as it allows to use OpenGL in a Java applet without requiring the website visitor to install JoGL or allow insecure access.
I can guarantee this would not work in general; on the Mac at least you can't just pass OpenGL contexts across processes, and most of the major browsers now on the Mac run plugins in a different process from the web page.
Chrome implements WebGL through Direct3D on Windows. So that's never going to work. There is no guarantee that any WebGL context is being implemented on top of a desktop OpenGL implementation.