foundation-topbar-menu.php and foundation-topbar-walker.php should be required in the WordPress functions.php file.
The code in foundation-topbar.php should be added below the body tag in header.php
Setup a menu in WordPress admin under Appearance > Menus
Use the 'label' class on a menu item to create a menu section title
Foundation Top Bar Doc: http://foundation.zurb.com/docs/components/top-bar.html
This hack fixed the above problem for me, though for some reason, I still can't get the menus to display correctly:
$element->has_children = !empty($children_elements[$element->ID]);
$classes = $element->classes;
$classes[] = ($element->current || $element->current_item_ancestor) ? 'active' : '';
$classes[] = ($element->has_children) ? 'has-dropdown' : '';
$element->classes = $classes;