Earlier quoted context omitted.
Even if Firefox were a monopoly, content owners would still desire DRM. Without the option to deliver that in harmony with HTML5, they'd just continue to use Flash, Silverlight, etc. We don't need counterfactuals to imagine a world without EME; we've lived it.
Flash and Silverlight were both dying before EME existed. Basically all it took was for Apple to say "no Flash" and Flash was as good as dead. I don't understand why you think that a free software infrastructure with a strong market position would be incapable of doing the same thing.
You might as well say, if the developer community got its act together and stood on principle, no company could caputure 'market share' without their consent.
The problem is not the Mozilla non-profit knuckling under -- it is developers failing to have an institution similar to other professions, such as the Bar or AMA, giving them principles.