"I think Firefox also has the advantage of being Netscape Navigator's spiritual heir. Lot of people who used NN (when it was good), got used to it and were keen to keep on using it over alternatives."

There were years between the last good Netscape Navigator and the first usable Mozilla, let alone Firefox 1. I really doubt there was that much loyalty during that long dark spell, especially since during much of that period, Internet Explorer was pretty good.