gfxWindowsPlatform forcibly enables and uses direct2d even if the user explicitly removes it from gfx.{canvas,content}.azure.backends. I'm not sure if this is by design or not, but it seems wrong to me as you'd have to set direct2d.disabled to stop d2d from being used at all. Personally I think gfxWindowsPlatform should honour the backends prefs as well to determine which things should be used where. One place where this could be useful is for things like testing Skia on modern Windows, especially if we want to test things like DWrite support in Skia.

As discussed on IRC.