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)
Not all HMD's supported by OSVR are capable of running in direct mode. To support these HMD's, Firefox needs to present the WebVR output in a window covering an area of the desktop specified by the OSVR server's json configuration file.