@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain("my.yahoo.com") {

#ad-lrec {
visibility: hidden !important;
width: 0px !important;
height: 0px !important;
padding: 0px !important;
border: 0px !important;
margin: 0px !important;
}
}