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)
This is a meta bug for having the ability to start/stop profiling, view profiles, etc in tree without any addons.
Would probably have this pref'd off by default? But either way, it should be available in all releases and custom builds.