Ok that puzzles me. For me, long/slow clicks were guaranteed to fail every time using the old method (onclick). Short ones had a higher chance. Using the new method (onmouseup), they work every time both in FF and Opera. Short clicks, long clicks, dragging clicks. (Even right clicks, will fix that later)
However, I did manage to indicate the control surfaces a little more obvious. How does a hand pointer and underline on hover work for you? I also added a confirmation to the delete control.