With recent build of libdrm (2.4.93) Mozilla Firefox cannot use accelerated
WebGL, use software emulation instead.

HW. AMD RX560 and AMD WX2100 (RX550).

SW. Ubuntu 16.04 with kernels 4.17.X and 4.18.rc from
http://kernel.ubuntu.com/~kernel-ppa/mainline/, plus Oibaf's PPA builds of drm,
mesa, etc. https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers

Symptoms. Firefox works OK, but on site with WebGL it works very slow - due to
fallback to software GL rendering.

Note. about:support page in Firefox DOES show correct driver info:
WebGL 1 Driver Renderer X.Org -- AMD Radeon Pro WX2100 (POLARIS12, DRM 3.26.0,
4.18.0-041800rc6-generic, LLVM 6.0.1)

But, on WebGL site (ex. windy.com), swrast_dri.so get loaded and eats all CPU
cores.