has WebGL been disabled?

"WebGL can reveal information about the video card in use, and high precision timing information can be used to fingerprint the CPU and interpreter speed." [...] The adversary simply renders WebGL, font, and named color data to a Canvas element, extracts the image buffer, and computes a hash of that image data. Subtle differences in the video card, font packs, and even font and graphics library versions allow the adversary to produce a stable, simple, high-entropy fingerprint of a computer. In fact, the hash of the rendered image can be used almost identically to a tracking cookie by the web server. [...] WebGL is fingerprintable both through information that is exposed about the underlying driver and optimizations, as well as through performance fingerprinting.

Because of the large amount of potential fingerprinting vectors and the previously unexposed vulnerability surface, we deploy a similar strategy against WebGL as for plugins. "

https://www.torproject.org/projects/torbrowser/design/