Jeff Muizelaar mentioned that WebGL 2 is now enabled within Firefox nightly builds. The WebGL 2 implementation isn't yet fully complete, but is at least to a point that it's working well enough for most modern content written against the provisional specification. Jeff mentioned it in this blog post.
Where as WebGL 1.0 is based on OepnGL ES 2.0, WebGL 2.0 is based on the more-modern OpenGL ES 3.0. WebGL 2.0 has been in development since 2013, however, the official specification has yet to be ratified. Back in August we heard WebGL 2.0 might ship before year's end, but alas that didn't happen and similar to Vulkan has slipped into 2016.
Mozilla had already been working on WebGL 2.0 support for a number of months. WebGL 2.0 should be widely-adopted in part because Microsoft tossed their weight in the WebGL working group.