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)
We're moving to a model where the cross-compartment wrapper map is represented as separate maps for each target compartment. This should give us a couple of opportunities to optimise wrapper map traversal during GC.