I haven't looked at your code closely, but...
Absolutely positioning between IE and Mozilla (and Safari) are a couple pixels off. This is because, as I understand it, one browser sets the absolute by the HTML tag, the other by the BODY tag. While this shouldn't make a difference, it does. There are also differences if you start using borders, padding, margins, and so on - each browser handles the additional space that each element takes up a bit differently.
You can try setting your HTML and BODY tags to have borders of 0. If that doesn't work, then you may want to change how you're doing your absolutely positioning. I prefer to use relative positions. Basically, it allows you to anchor an absolute position to another element or section of the page. First, you declare an area you want stuff to appear absolutely inside of, relative. Then do your regular positioning inside that, then close them all off. Something like the following:
DIV style=position:relative;
DIV style=position:absolute; left:10px; top:20px; width:200px; height:200px;
/DIV
DIV style=position:absolute; left:10px; top:210px; width:200px; height:200px;
/DIV
/DIV
That would create two content boxes, 200px by 200px, 10 pixels apart, set 10 pixels from the left border of the initial box.
I realize that's about as clear as mud. A great site to get some CSS tips is Eric Meyer's site: http://www.meyerweb.com/eric/css/
Another option is to use some sort of browser detection, then set up separate styles for each browser. Its ugly and a pain to maintain, but it does work. I find myself forced to do that more than I care to admit.
-Kris