Oh, IE is rendering it incorrectly. Firefox is doing what it should. In absolute positioning, an element is removed completely from the normal flow of the page. It is, in effect, independent. It will not respond to the width of the browser. You shouldn't be using positioning like that as if the browser window gets too small, part of the design goes off the screen where it's inaccessible. Try using the margin: 0 auto; or another method for centering and you'll have a fluid design.