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)
ReadPixels should also no longer need a dummy IDL stub, since there's only one valid set of arguments. I have had trouble actually removing the stub, but the functionality is the same just leaving it in.