For the first few years, there were lots of sites that were designed for IE that broke in Firefox. Thus, at first, it was actually worse for many people. Yet, because the early adopters kept pushing it on everyone of their malware-ridden friends and relatives, it grew in usage anyway, allowing Mozilla to afford to make it better.
I was one of those folks who contributed to the Firefox announcement ads, but I don't really believe that it succeeded because folks pushed it rather than it simply being a better product. Yes, some sites at the time worked better in IE, but on the whole, the experience on Firefox was better and that's why folks supported it, not because they disliked Microsoft or something. (And yes, because we support proper web standards.)
Firefox was a spinoff of Mozilla and was a pretty good browser from v1, and within a year of release was considered the best browser available.
