Most of old add-ons for Firefox cannot work with Firefox Quantum
Most of old add-ons for Firefox cannot work with Firefox Quantum. The most important advantage of Firefox is customize add-ons now is gone with Firefox Quantum. New version of Firefox now cannot customize, add, edit, delete right click context menu. If Firefox don't change this, we as Firefox users will leave Firefox to use Chrome.
Alla svar (3)
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
