Disable "Select All" menu item, if alredy selected all items
(#3)
Add note about richlistbox.selectAll()
See https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/richlistbox
"Note: In versions of Firefox prior to Firefox 3, rich list boxes support only single selection. Firefox 3 introduced multiple selection to rich list boxes."
But all works fine for me...
(#3)