During the developer meeting today, and a subsequent IM conversation, I became aware of an interesting conundrum: if IE 6.0 weren't as standards-compliant as it is, Firefox never would have become as popular. Think about it for a second: if IE 6.0 were as bad as 5.0 or 5.5 (or as bad as people seem to think it is), major websites never would have made their sites work in Firefox. Making two different versions of a site (the IE version and the correct version) is too expensive, so they have to choose, and obviously the one that >= 99% of web users would use is the one the company should spend their money on. Thus, Internet Explorer would have retained market share because nobody would have made their sites work in Firefox, and users would not have had a very compelling reason to switch. It's the fact that IE's behavior was so close to correct that allowed people to start using Firefox.
Internet Explorer was a pioneer in the things that web developers today care about: it supported CSS for cleaner, more efficient coding, it supported XML and XSLT to bring data together from any number of sources and transform it into useful content, and it supported a variety of "active" technologies to make thin clients possible. No other browser at the time could even come close. It's a testament to how innovative Internet Explorer really is/was that only now do we really have a browser that can do approximately as much approximately as well, years after nearly all development on Internet Explorer stopped.