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)
Now that we are done with our 'security by default' project we should update the documentation. In particular, we should add the interaction of loadingPrincipal, triggeringPrincipal and principalToInherit.