One In Six Uses Firefox
According to Amsterdam-based OneStat, in US less than 80% of browsers used are Microsoft IE's (2.1% less in one month), and more than 15% for Firefox, an increase of 1.1% in just one month.
Maybe it's time for Microsoft to release Internet Explorer 7 or give up!
In Europe we are still apparently big IE users, except maybe of Germany, a leader in open source software.
So should I start to program only for Firefox by now :-)