Mozilla could have promoted a better DRM media player that is not part of the web. They chose to promote the EME adding DRM to the web.
Exactly Mozilla could have added the EME but with extra features that save the content, thus demonstrating to the web community that it is open to innovation and not a space for land grabs, and not compatible with DRM. The contemporary web is open, without specialized DRM support, and free to innovation, and Mozilla's actions are compromising this, this is a very dark development. Mozilla's support for the EME is support for selfish corps making land grabs on what we can implement in our own web browsers and under the threat of persecution, and they have damaged the open web.
Mozilla are not just supporting DRM, you could already view DRM media, the significant development is their supporting for the addition of DRM to the web in a claimed standard, a damaging development for the open web. Mozilla had the choice of supporting the viewing of DRM media outside the web, by using a plugin or by using a separate media player. The DRM web interface they have decided to support, the EME, in not even capable of playing media on it's own, it is just part of a play and the rest is proprietary JS supplied by the content distributor. This is a strategy promoted by the distributors to advance their own selfish interests, by Netflix/Google/MS, it locks the user into using the distributors web based media player, is anti-competitive, and damages the health of the open web market. By supporting the EME Mozilla has made it almost impossible for the open web community to promote alternatives, damaging the open web community, in an act of betrayal.
Mozilla made no attempt to promote alternatives, have not explained the technical details of their EME/CDM design in enough detail for their claims of user security and privacy to be verified, and have refused to clarify that users can even view DRM media via Netflix in all its glory using their EME/CDM which was a key claimed reason for their decision, and have not been honest in the reasons for their decision (it's is not about supporting the viewing of DRM media because this is already possible).
While people are free to not use the DRM option, Mozilla are supporting the addition of DRM to the web using the EME specification. This is a damaging development, it's not just a generic plugin API but an API focused on DRM. If you add a save-as button feature to an implementation of this open web specification then you risk being prosecuted. Also where does it stop, Mozilla could use the same rationale to support all DRM additions to the web.
With Mozilla supporting the EME it has become practically impossible for any other standard to compete. Standards that are not driven by corps like Netflix/Google/MS and that could have offered the user better security and privacy and features. For example a simple and general declarative HTML extension that can tag the media as requiring a DRM media player which the browser could use to launch an external player keeping DRM out of the web. Mozilla's decision makes them the enemy of such efforts. They have betrayed the open web community.