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)
In an input field that isn't wide enough to hold all the text in it, we should be able to scroll left/right with two-finger swipes. The input field is scrolled for a few pixels before it stops and navigation kicks in.