The fact is that DRM is in the HTML spec now. It’s not likely to leave the spec, even with massive objection from everyone. It got into the spec initially over similar, massive objection. That’s done. Mozilla has two options: refuse to participate or adopt and improve.
In the past (e.g. with h.264 or WebSQL), what’s happened is that they have refused to participate and floated their own, open, alternative approaches. The result has usually been that the proprietary implementations (in many cases already de facto standards) have gone ahead anyway, gained user and developer acceptance and Mozilla has later had to back pedal into supporting those or risk losing their users. What’s more, not participating in initial implementations in the past has left them unable to influence the nascent standards and the implementations suffer as a result. Anyone who has ever tried to use Web SQL for anything can certainly attest to that.
This time, they have opted to take a seat at the table, participate in the initial implementation, yell obscenities as necessary, call out the bullshit as it is floated into the evolving spec by proprietary interests, and influence the implementation’s future. This also has the neat side effect of letting people continue to use Firefox to do all the inherently proprietary, currently-plugin-based things which have become normal and expected things to do on the Web, like watch Netflix. And all of this without yet another plugins governed by single corporate entities, which are certainly not good for the Future Web.
Tim Berners-Lee ensured this would be a lose / lose for Mozilla and for the Open Web last year when he came down on the side of DRM and it went into the spec in the first place. It is a bummer, it’s almost certainly the objectively wrong thing to do, but I’d definitely rather have Mozilla in the conversation and bringing the fight directly than locked outside holding a protest sign while Comcast is in there with donuts and a suitcase full of brand new thirty dollar bills with George Bush’s picture on them…
The Web is changing, but that’s not new. It has always changed and it will continue to change. More great things will happen. More terrible things will happen. The critical thing is to continue to participate. Ditching Firefox in protest (for… which DRM-free browser, exactly?) is not actually helpful, and likely hurts the cause in the long term. But you know what? It’s the Web: at any point, if you don’t like what’s happening with the browser scene, please write a new one!