I mean that their fears are not (necessarily) misguided, and claiming them to be is not helping the FSF's argument. I would rather they focus their arguments on the real reasons to avoid DRM, rather than making unverified claims about Mozilla's motivations.
How are they supposed to verify a claim like that in advance? Their market share is dropping already, that's about as rigorous as you can get without forking the universe to run some tests.
Not from lack of EME. EME isn't nearly widespread enough to have any impact. Netflix still runs just fine in Silverlight.
In the absence of evidence, I don't see how claiming those fears are misguided is any less valid than claiming that they are well founded. I'm not really sure what argument you're making here.