@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

.toolbarbutton-1 dropmarker  {
opacity: 0 !important;
}
.toolbarbutton-1:hover dropmarker {
opacity: 1 !important;
}
.toolbarbutton-1[disabled="true"] dropmarker {
opacity: 0 !important;
}