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

#btn_undoclose,
#btn_undoclose toolbarbutton {
min-width:0 !important;
}
#btn_undoclose {
-moz-image-region: rect(0 40px 16px 24px) !important;
}
#btn_undoclose:hover {
-moz-image-region: rect(16px 40px 32px 24px) !important;
}
#btn_undoclose[disabled=true] {
-moz-image-region: rect(32px 40px 48px 24px) !important;
}
#btn_undoclose .toolbarbutton-text {
display: none !important;
}