A more complete description of the backend combinations is at [[Platform/GFX/WebGL/Backends]].
Currently, we lack composition acceleration on WinXP, most Linux, and Mobile.Mobile is and Linux are being investigated as part of OMTC.Linux just needs better OGL driver support to allow unblacklisting.
WinXP can't run D3D10 to take advantage of ANGLE's EGLSurface sharing.