FireFox / IE6 CSS problem

Hey all ?? I got a problem on the following site:
https://www.verootjuh.nl
If you check it with IE it is all good
But FiFo shows it all foked up ??

Here are the CSS info on both sidebars:
RIGHT SIDE
#sidebar
{
position: absolute;
padding: 20px 0 0px 0;
margin-left: 65px;
width: 180px;
border: 1px solid black;
}

LEFT SIDE
#sb_left
{
position: absolute;
padding: 20px 0 0px 0px;
margin-left: -690px;
width: 180px;
border: 1px solid red;
}

Now I know the problem is the -690 vs the 65 margin-left.

Now here comes the big Question:
For some reason IE uses a margin from the CENTER side on
but FiFo uses a margin from the LEFT side on…
So on IE it looks good, but FiFo has the problem that a NEGATIVE margin shows outside the page…

A little example of what I mean:
IE6:
-700————0————-+700
|————–CENTER———–|
FiFo:
0————-+700——–+1400
|————–CENTER———–|

So somewhere for some reason there is probably something wrong why IE all of a sudden uses an alternate reference…..

Anyone had this problem before and has a solution ??
You can find the used STYLE-SHEET at:
https://www.verootjuh.nl/wp-content/themes/veronique/style.css

Thnx a lot for anyone who can submit a hint here ??