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)
Sometimes our blob images are so small that it's not worth having a retained image for them. In this case it's better to just include the image inline in the display list to avoid the extra IPC work of retaining it.