34572 - Use native context menus on Mac OS
Use native context menus on Mac OS Categories Core 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) User Story 21 years ago Mozilla on MacOS is using native main menus -- the XUL menu items are being translated into native menu structures, allowing Mozilla to use the Mac's main menu bar. Why couldn't this be done with context menus as well? As far as I know...
Source: mozilla.org