Netscape Navigator had substantially beat IE as a first-mover in the market and the mind.
IE wasn't a first-mover, it was bundled with the computer, it won as the most available, just like Starbucks vs. Coffee Bean - later comers can be assumed as more readily available then their perceived equivalencies. Firefox broke through by shattering the consumer's perception of equivalence.
The door for differentiation in the same way as before has closed, but not for differentiation in other ways that people immediately perceive.
Lacking a prescriptive direction that Mozilla Inc should take to establish this doesn't invalidate the observation, you can describe an illness without knowing the cure.
IE wasn't a first-mover, it was bundled with the computer, it won as the most available, just like Starbucks vs. Coffee Bean - later comers can be assumed as more readily available then their perceived equivalencies. Firefox broke through by shattering the consumer's perception of equivalence.
The door for differentiation in the same way as before has closed, but not for differentiation in other ways that people immediately perceive.
Lacking a prescriptive direction that Mozilla Inc should take to establish this doesn't invalidate the observation, you can describe an illness without knowing the cure.