overflow:hidden

For the examples demo, on FireFox 1.6a1 (Gecko/20051008) I see scrollbars for evey column heading. May be it can be suppressed with overflow:hidden

If not activewidgets.com issue please file bug at https://bugzilla.mozilla.org/

Yes, this is a known problem.

http://www.activewidgets.com/general.faq.browsers/gecko.html

Here is temporary fix until FF 1.x is released:

.active-grid-row.gecko, .active-box-normal.gecko {
overflow-y: visible;
}