Both can be true. Progressing without innovation only works when your product is Coca-Cola or Bic lighters. FireFox as a name or brand is nowhere near it's former v1.0-3.0 glory days.
It was the alternative to IE6, the first rays of dawn bringing hope to to a desolate, war-torn funereal valley of culpable corporate complacence.
Hatred for IE6 drove people to Firefox more than anything else - IE was horrible. Firefox users crowdfunded a two-page ad in the New York Times, mostly to get people to move off of IE6.