Firefox WebExtensions vs Add-on SDK

Question

I've been trying to figure out the difference for hours and have drawn no conclusions.

Are both methods used to develop add-ons? Are they independent or connected development methods?

Thank you for any clarification.

Answer 1

Moved to solution:

This page is just a draft, so just use it as a pointer -

https://developer.mozilla.org/en-US/User:wbamberg/Add-ons