It's not that Mozilla named their UI "Chrome", but that "chrome" is a graphical user interface word. For a browser it refers to the stuff around the web page content, but it's more general than browser use (you could refer to Blender's chrome around the 3D viewports to refer to its toolbars, etc).
i.e. https://developer.mozilla.org/en-US/docs/Glossary/Chrome
Ironically, the modern web also led to UI chrome being harder and harder to distinguish even in native applications.
My apologies for editing my comment and breaking your [3] reference. I'm trying to imagine just how much work it would be to enable footnotes in comments that others can link to. It would be nice but quite the effort to get right, and I'm sure people would prefer other features first such as more formatting. (or a full implementation of Emacs in the editor window with org-mode as the markup language, with citation links. lol!)