IE never fails to surprise me. Look at the following code for example.
document.getElementById("someId").innerHTML = "<li>Some content</li>";
This code has surprising results in Internet Explorer and Firefox, and I haven't found a decent explanation on the Internet of what exactly happens, so I'm posting this out of utter surprise.
First thing you'd notice is that someId is a paragraph (p) tag. Secondly we are inserting a list item (li) into this paragraph, without having a unordered list (ul) as a parent element of this list item. If you are really the kind of markup nazi that I am, you'll notice that the p tag doesn't allow any block-level tags within it, and both LI and UL are block level tags, which is not permitted by the W3C rules.
So, how do browsers react to this?
Firefox does some code cleanup (I guess), and renders what looks and behaves like a list item, complete with a bullet and stuff. (Interestingly, it assumes that it is an unordered list and not an ordered list. Wonder why that's the case.)
IE's not 100% percent correct, though. It looks like it only enforces block/inline tags and not really tag semantics. Which means if you change the p to div, the code will execute correctly, since the div element allows other block-level tags within it. So, IE doesn't seem to be perfect, but seems to be kinda stricter than Firefox. Which may or may not be a good thing.