The Canvas 2D code has an optimization where it tries to switch the rendering mode from software to OpenGL is a sufficient number of certain operations are used. Once this happens, drawImage does adequately check if there is an available GL context before trying to use it. The result is that the mochitest dom/media/test/test_bug879717.html (and probably several others) fail. The problem originated with bug 880114.
Created attachment 8683755 [details] [diff] [review] verify that a Skia GL context is actually available before trying to use it in Canvas2D drawImage