Use sane about:config value: webgl.disabled = true

While reading through various about:config security hardening guides, I found several bad default values for the Tor Browser:

• webgl.disabled = true
  • WebGL is a potential security risk. Although disabled in the TBB, this can be set to "true".

(This issue was split from https://trac.torproject.org/projects/tor/ticket/27059)

Trac:
Username: floweb