It can be different in browsers though. One time I found a site that would display something showing how it would look in different browsers. It was amazing.
I never have been able to find that site again, even in a search. There are so many different browsers now that maybe the site disappeared!
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.