WebGL2 does not work after update

I'm running Firefox inside VirtualBox machine with Direct3D enabled. WebGL in version 61.0 x64 was working fine only with "webgl.webgl2-compat-mode=true". After update from 61.0 to 62.0 (x64) WebGL 2 became disabled. WebGL test on browserleaks.com reports "This browser supports WebGL 2: False (supported, but disabled in browser settings, or blocked by extensions)" I did not install any extensions, also checked config "webgl.enable-webgl2=true". Also I tried changing "webgl.webgl2-compat-mode", it does not affect the problem.