Whenever people talk about how IE ruined the internet, I think about AJAX. I actually thought IE was great for the web. A poignant example I remember was, if you got a /TR /TD out of order, Netscape wouldn't show the web page at all. It'd work fine in IE though.
IE just made it so much easier to move fast in web development. People blast IE, but I really don't think the web would be as good as it is today without it.
Contrast that with what Chrome has done to the web. Not good.
AJAX is the one feature people can point to as something good that came from Internet Explorer. That and maybe their take on the box model. But virtually everything else they got wrong. Worse yet, they got complacent with their lead and web development stalled for years as a result.
Other browsers have done far more to get us to where we are.
Chrome introduced a modern security model and many useful APIs and protocols (including HTTP/2). Firefox popularized the concept of browser extensions and developer tools like Firebug. Safari made much possible by opening WebKit, such as Chrome and mobile browsers. Opera invented half of the original browser concepts including tabbed browsing.
AJAX was largely responsible for the initial push to modern, dynamic websites, but it doesn't score enough points to make Microsoft the good guy in this history.
AJAX has been bad for the web. Letting Javascript make requests without explicit user action & vetting of whatever it's sending is basically the reason the web's so messed up and user-hostile.
Even the earlier methods required JS to be able to trigger requests not explicitly intended by the user. And at least they usually fired up a loading bar at the bottom of the browser, so you could tell shenanigans were happening.
AJAX made that cleaner and broadened its use, but yes, you could already make requests with Javascript that the user didn't want you to or didn't care to make for any purpose of their own.
IE just made it so much easier to move fast in web development. People blast IE, but I really don't think the web would be as good as it is today without it.
Contrast that with what Chrome has done to the web. Not good.