Comment 21 for bug 1583849

Note that with commmenting out the gfxCriticalError() in this function and in the next, like:

static inline cairo_content_t
GfxFormatToCairoContent(SurfaceFormat format)
{
  switch (format)
  {
    case SurfaceFormat::A8R8G8B8_UINT32:
      return CAIRO_CONTENT_COLOR_ALPHA;
    case SurfaceFormat::X8R8G8B8_UINT32:
    case SurfaceFormat::R5G6B5_UINT16: //fall through
      return CAIRO_CONTENT_COLOR;
    case SurfaceFormat::A8:
      return CAIRO_CONTENT_ALPHA;
    default:
// gfxCriticalError() << "Unknown image content format " << (int)format;
      return CAIRO_CONTENT_COLOR_ALPHA;
  }
}

makes it mostly work, only a full clienat area black flash every now and then