Problem with firefox and a dhtml-menu

Hello.

I am using the dhtml-menu from www.brainjar.com. Directly below the
menu-bar i placed an i-frame. In IE everything works fine. But Firefox
closes the menu right when i move the mouse-pointer over the opened
menu and the mouse enters the i-frame area. You can see an example at
http://www.stuckenholz.biz/test.html.

Do you have an idea how to fix the problem?

Thank you.

Alex