Mozilla is very upfront about the fact that it goes against their principles. https://hacks.mozilla.org/2014/05/reconciling-mozillas-missi... Anyway it's opt-in, it's easy to uninstall the one CDM it comes with, and it's fairly easy to stop it from even asking about downloading CDMs. The EME-free build just does all of that for you up front.
A well-hidden build of Firefox to silence the people who accuse the Mozilla Foundation of betraying their principles...