The chicken-and-egg is a valid argument. But it applies to Linux as well (no users -> no apps being ported -> no users).
Linux does suffer from the issue of low market penetration, but it's always had a relatively low market share (and its actually getting better as of late).
Whereas firefox has been on a steady decline for nearly a decade due to incompetent management with conflicting goals, something that's unlikely to change anytime soon.