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

#markAsReadButton[disabled="true"] {display:none;}
#markAsUnreadButton[disabled="true"] {display:none;}

/*
#markAllAsReadButton[disabled="true"] {display:none;}
#markAllAsUnreadButton[disabled="true"] {display:none;}
*/