Rosali, im surprised you have a problem with FF. Although I dont have 3.6.3, but 3.6.4/5/6 work ok it seems.
Anyways, could you try if this fixes the scrollbar?
#compose_addressbook_container {
height: 365px;
overflow: auto;
overflow-x: hidden;
}
Should be changed in skins/default/compose_addressbook.css , i added the overflow-x.
I cant reproduce the overlap
Hmm, maybe a font issue?