[throwaway2016a]

You contradict your part here. I'm not sure if you meant to because the rest of your post sounds like it is saying Mozilla needs to pin if it's using a custom signing mechanism.

> Firefox uses (and ships with) the Mozilla Root Program

> can not not pin certificates

Shipping with a certificate store is by definition, pinning. So not only can it but your own post states it is when it says "and ships with".