That's a screaming headline, but not a lot of meaning within. Actually, I understand what author is trying to say, but it's pretty pointless. Yeah, I also see a problem out there, but it's a little deeper than "only Mozilla understands".
Open Source Software is there because somebody is writing it, software isn't going to write itself. And mostly it's alive not (at least "not only") because somebody is financing it, but because there are people that both can and want to write it. And, oh, I should've said "make", not "write", because making it is so much more than just writing it. Especially when we talk about general purpose client-side apps author cares about so much.
And here we have problems with both "can" and "want". Generally, people that are actually able to write software prefer slightly different stuff from your "typical end user". Actually I don't know a single browser that I would still like and it's pretty obvious that your "typical user" won't be so much delighted by my beloved CLI apps.
But what really makes me sad is that "can" problem. There might be enough of those who can do some simple coding in community, but it still takes large company to hire somebody who will cooperate with programmers to make beautiful design for their app or some folks that can do some serious math/programming. FOSS apps still generally suck in terms of UX and visual design (at least for that typical end-user). There's no FOSS that could compete against Photoshop or Cubase or be even close to quality of Google's text-to-speech services.
Of course there's no one to blame except ourselves, but if you want to see the problem — here it is. It's about us improving our skills to be able to build something outstanding, to build it for free and make it open source.