The only differences I know between IE and Firefox is, Firefox isn't as forgiving with some CSS as IE is. In fact, Firefox is more strict in it's adherance. IE has always had that forgiveness factor "built in" as it were. So even sloppy code will render near-perfect in IE, and just looks sloppy in FF.
LOL, you just had to go and tell me that when I thought I was getting so good at HTML!!