Question : Firefox displays vertical scroll - IE doesn't

I have my code ready to deliver.  It works great in IE.  When I looked at it in Firefox, the screen height is reduced and there's a vertical scroll bar.  Ouch.

What can I do to display it properly in Firefox?  Any ideas on where to look?

The code is 850 lines long so I won't post it.  But I have screen-shots that I will attach.
The program is written in PHP.

Naturally I suspect a CSS issue -- but after changing it for the past 5 days, I can't find a solution.  Any suggestions?
 

screen-with-ie.jpg (185 KB) (File Type Details) 

Display using MSIE -- works good

screen-with-firefox.jpg (88 KB) (File Type Details) 

Display using Firefox - does not give full height

Answer : Firefox displays vertical scroll - IE doesn't

You have "#main_div" in your CSS file twice.  I killed "overflow: auto; height: auto;" and the scroll bar went away.  You also have a missing end tag for the header div </div> on line 52 of the "View Source".  There are still spacing differences between IE and Firefox.