I don't think the parent's point was about purity of not having DRM in firefox, but rather that since Firefox's user base has decreased so much in recent years, Mozilla no longer has the leverage they used to in terms of browser features. In other words, if Firefox had 50% share of browser usage, they would be in a position to prevent EME from becoming an industry standard -- but since they have a much lower percentage (10% I think if you take mobile into account), they felt forced by pragmatism to include it.