Do you mean add-ons from 2017 and earlier? Sorry if this sounds blunt, but that ship has sailed. What we need is a built-in menu editor. I have no idea if/when we might get that. Mozilla has a site at https://connect.mozilla.org/ to gather input on new product features. You can search in the Ideas section for a similar request and vote for it, or submit a new one. Meanwhile, if you are a bit hackerish, you could look into using a startup script (AKA userChrome.js) to inject something like the old keyconfig extension into Firefox through a back door. I suggest asking on https://www.reddit.com/r/FirefoxCSS/ for information along those lines. I have a general article as an introduction: https://www.userchrome.org/what-is-userchrome-js.html

Here's an existing Idea post you can vote up, and feel free to comment about your use case as well. https://connect.mozilla.org/t5/ideas/customizable-hotkeys/idi-p/4979

See also https://github.com/stonecrusher/simpleMenuWizard