webgl.min_capability_mode might be too minimal

We set webgl.min_capability_mode in an effort to resist fingerprinting. Unfortunately, it seems minimal mode might be a little too minimal. It completely breaks the HexGL racing game (at http://hexgl.bkcore.com/play). We should try to figure out what exactly about minimal mode is breaking this game, and make a guess as to if it is really a fingerprinting issue.

Given that my 4 year old laptop with Intel built-in graphics was completely capable of playing this game with this pref unset, it seems that maybe webgl.min_capability_mode is a little too minimal, and could be altered to represent a slightly less restrictive set of capabilities without much fingerprinting risk.