This is the way. Turning off features only to unclutter a menu is silly and I can't believe there's not more pushback than your post here. userChrome.css exists for this exact reason, mucking about in UI without mucking about in feature machinery. I guess a text file and some CSS is just too hard many HN users.

Important for macOS: You must set "widget.macos.native-context-menus" to "false" or else you can't inspect/modify the context menu through userChrome.css.

The other great use for userChrome is reclaiming the space at the top of the browser if you use tree-style tabs. With just the url bar, the window is close enough to full-screen when I close the tab tree that I rarely feel the need to use F11.