Combo Box dropdown dispalys differently in FF then IE

Alex;

I have a combo box on a form located at the bottom of the HTML page. On IE the Combo control detects that it is at the bottom of the window and displays the dropdown on top of the control. In FF it displays below the combo control and forces a scrol bar to be displayed in the browser window. Is there a way to force the dropdown to display on top of the control?

IE 7
FF 2.0.0.16