You really think Firefox was ever going to be in a similar position to Windows? The two situations aren't even remotely comparable.
Opera has always been a bit fringe like linux (while still being good). IE.. well enough said. Safari was a decent choice on mac for a couple years before Chrome.
Thats where my comparison to windows resides. It was the only decent option. It took OSX a big part of the 00s to reach mainstream dominance over Windows XP.
Also OS X has never reached mainstream dominance over Windows.
demographic = 'the HN crowd'
mainstream_OSes = ['windows', 'mac']
sorted = sort_by_popularity_within_demographic(mainstream_OSes, demographic)
dominant = sorted[0]
IE's rendering engine and JS/CSS, to be more precise. (Look at the IE6 in Longhorn pre-releases and IE6 in XP SP2)