This is (I guess) a problem with the z-index stacking order, so a quick look in the documentation and this forum showed several things you can do to solve it, but I've no luck with it. Because I can't give access to people here for Livelink (we don't create accounts for external users), I have created a page on our server with simulates the problem. I've tested it with Firefox and Internet Explorer, the results are the same.
Livelink creates pulldown menus by writing a table with an item in every cell. This table is put in a DIV which is invisible, but becomes visible after clicking on the menu header. This is what I've simulated in the following page:
http://www.rssd.esa.int/COMP/LIVELINK/ll.html
As a menu I've used one of the Milonic examples. If you click on the link show/hide menu, you'll see that the table in the DIV is written under the Milonic menu.
I've tried various options like adding zIndex=1000 to the .js file that defines the menu, but so far I had no luck. I hope somebody can come up with a clever idea.

Cheers,
Martin