TFA pretty much summed it up with:

  Completely useless. Thanks for showing me every feature you’ve ever shipped

And that's what it is, we'll just use the right-click menu as a garbage dump for every feature we've added. I've currently got my right-click menu down to eight entries, of which four are extensions I added (NoScript, DownThemAll, etc), and the four built-in ones are things I've never, ever used in 20+ years as a Firefox user. I'm also running RightLinks which turns right clicks on a link into "Open in New Tab", which is what I want to do, oh, approximately 100% of the time I right-click on a link (for the epsilon times I don't want to do that you can override with Ctrl-Click to get the original menu back). Its actually painful watching users who haven't overridden the Firefox builtins use right-click, "right-click, scroll, scroll, pause to check, scroll, click".