The divs below both use the same background image, centered horizontally and set to repeat vertically. When resizing the browser window, the background images should remain properly aligned. Firefox 3 will misalign the background images at certain resolutions - most likely due to a rounding bug for placing horizontally-centered elements.
<div id="wrapper">
<div id="centered-800px">
</div><!-- /#centered-800px -->
</div><!-- /#wrapper -->
<style type="text/css" media="screen">
/*<![CDATA[*/
#wrapper {
background: url(centered-background.png) 50% 0 repeat-y;
}
#centered-800px {
background: url(centered-background.png) 50% 0 repeat-y;
width: 800px;
margin: 0 auto;
height: 470px;
}
/*]]>*/
</style>