Microsoft was also first to the table with DHTML, or what we now call DOM manipulation.
The combination of DOM manipulation and asynchronous HTTP was like crack for developers, and resulted in an explosion of IE only business apps, which caused IT departments to become IE-only, which led to a feedback effect.
All the crappy IE-only back-end systems that still fester in enterprises today hark back to those days.
Chrome/Firefox/Safari all do a pretty good job of rendering HTML consistently - we've come a lot further than where we were in 1997, when websites commonly had "Made for Netscape" or "Made for IE" graphics on them.
Fun fact: AJAX came from an extension to the browser from Microsoft (first written for Outlook web client). For all the talk about standards and open source, I find it ironic that what is possibly the most defining feature of today's web came from what at time was the greatest force against standards and open source.