The code is 100% open source, so even if there isn't a GUI option for it, it would be easy for people to make builds without it. There are already many forked builds of firefox like iceweasel, etc.

Yes, I expect such thing to surface, but it would be nice if Mozilla could provide such options on their own too. That would be some small positive gesture towards those who don't appreciate their move and see it as a betrayal of Mozilla's core values. It would as well make this issue more apparent. Doesn't Mozilla care about educating the public on such matters? It surely would be a positive thing for the Open Web.

As the blog post mentioned, the EME stuff will be an option that the Firefox user would need to agree to install. That would be an opportunity to educate users on the topic, I think.

I meant it a bit further. Not just disabling the EME external module, but disabling all related code in Firefox itself on the build stage. While functionally it won't make much difference, it would have more of a symbolic nature of making a point. Plus such builds would guarantee that it can't even be enabled at all (without user's knowledge for example).

If there would be build switches to disable that, I'm sure Linux distros with similar to Debian policies will ship versions where it will be disabled altogether.