How can I compile Firefox from source which 1) Is Un-Branded and 2) Uses a custom Add-On Certificate

After unacceptable delays to the signing process for both Listed and Unlisted extensions I’m left with no choice but to look for other solutions in order to distribute extension updates to my users. In order to do this I need to do one of two things, either: encourage them to enable the use of unsigned extensions or: replace Mozilla as the signer of my extensions. Since encouraging the use of unsigned extensions is not acceptable, I’m left with no choice. I have to fork Firefox and use my own certificate to sign my browser extension. This is not a prospect I relish, running the infrastructure required to support a Firefox fork is not something I want to do. I want to be able to trust Mozilla to distribute the software I provide to my users, but I am rapidly losing that trust as my extension languishes in support purgatory and I receive absolutely no meaningful communication from Mozilla.

So how do I do this? Is there an option I can use in a .mozconfig file to configure it? I’d like to change as little code as possible, so I can track updates.