I'd argue that you shouldn't need third party add-ons plus modifications to both userChrome and about:config to do it, so it could be easier. A "Customize Context Menu" under Edit would be nice and easy for even regular users to discover and take advantage of.

Why is my Edit menu so long? What is this "Customize Context Menu" thing that I never use, or will use at most once a year?

Just kidding, but it does illustrate that there's always a tradeoff with these things. (I would like to have the ability to customize the context menu too, fwiw, though it's not as straightforward as the other customizable bits of UI since the context menu is, well, contextual.)