If content providers knew that there was a large chunk of users they'd be excluding by choosing the DRM option, they would be less likely to choose it. Firefox may be only 20% of web users, but that's still a lot of revenue to leave on the table if we can rely on firefox users to stick with firefox. I don't know whether or not we can - apparently, Mozilla is worried about it.
The best option might be to sink this development energy into something that will draw users from other browsers, if they can figure out what...
"Content is king!" Have you never heard that before?
You say Mozilla should figure out what will draw users from other browsers, but you've outlined what will draw users from Mozilla to other browsers. In the end, people want content. The content providers have more control. If 70-80% of the browsers already support the DRM they want to use, the other 20-30% will follow or be left out. Which is exactly what happened here.
There is tons of content on the web that has nothing to do with video. There is tons of video on the web that has nothing to do with DRM. If there is 20% of web surfers excluded by Netflix and Youtube, and DRM in fact doesn't matter for securing sales, then that's a huge edge for any new content provider that wants to compete with the incumbents.
All of that said, yes, of course this is something that will serve as a draw for users away from Mozilla. And yes, of course Mozilla might not be able to find something else that can serve as a better (or even comparable) draw that will not compromise their principles at least as much. I'm not casting aspersions at Mozilla and saying "Gee, they're dumb, why don't they just...". I'm saying "It would be better if they had found X" where I'm not at all sure such an X exists.
Oh, I don't know that they made the wrong decision - I have every expectation that they thought about this as well and decided it was too likely they did not have the clout. I said as much.
It probably will be once DRM/EME is available in every browser. At least the chances are increasing, and that's exactly why making DRM ubiquituous and easily accessible is such a bad idea.
The problem is not that Mozilla implementing EME removes leverage to force Netflix into abandoning DRM (this won't happen anyway anytime soon), the problem is that once DRM is readily available without a large technological investment and without losing too many users, virtually everyone will use it for virtually everything, simply because there is little to none incentive not to do it, from a publisher's perspective.
The best option might be to sink this development energy into something that will draw users from other browsers, if they can figure out what...