Shared components used by Firefox and other Mozilla software, including handling of Web content; Gecko, HTML, CSS, layout, DOM, scripts, images, networking, etc. Issues with web page layout probably go here, while Firefox user interface issues belong in the Firefox product. (More info)
There's a handful of things that can go wrong here, particularly in DeviceManagerD3D9::Init. It would be good to make sure that we're rejecting because the hardware really isn't supported and not because of an unexpected error.