Most people just want the damn thing to work. Studios, whether the EFF and others like it or not, are not going to be changing their stance on DRM any time soon. It seems that more and more media is being consumed on a subscription basis than is being downloaded (see Spotify, Pandora, Netflix, Amazon Prime, Hulu)... People are caring less about owning the content than having access to it.

Currently with DRM there are a variety of plugins to support it in the browser. You have to download Widevine's plugin, or PlayReady's plugin, or whatever. It's just a better user experience if we really do need DRM to have some standardized DRM that the browsers can implement to make it seamless for the user.

Note that I don't support DRM, I think it's a total waste of time because the movies aren't released to the wild by your average Joe who is downloading movies from Amazon. It just serves to hurt the average user. However I think that if we must have DRM, it should at least be something that is easier and works better for the average user.

To answer your question: the difference is that Mozilla is not going out and promoting DRM. They are being pragmatic and reasonable in the less than ideal situation.