Firefox 13 all dropdown menus are showing - 2

Hi,
I have a weird effect with Firefox 13, and only with the version 13+, and only on an online web site (still under construction): all the dropdown menus are showing, see the first image:





Firebug says "DropdownMaxMenu is not definded", but the Script is definitely definded.

the strange thing, it worked until Firefox 12, and it still works withe the same web site locally with Firefox 13...

Has any one an idea?