That would be very disappointing from mozilla! I only found a support-thread from yappy in 2016 but if this is still up-to-date there should be an outrage on HN's frontpage.

I also made a simple, private(!) extension before I learned about the signing-requirement and that it won't work without uploading it. So I canceled my career as an extension-writer and just went to bed angry.

They really fucked this up (without even mentioning the "armag-addon").