fire fox ハック

div.sample { background-image:url(img/bg00.png); }

div.sample, x:-moz-any-link { background-image:url(img/bg01.png); /* Fx 1.0 */}

div.sample, x:-moz-read-only { background-image:url(img/bg02.png); /* Fx 1.5, 2.0 */}

div.sample, x:-moz-broken { background-image:url(img/bg03.png); /* Fx 3.0 */}

div.sample, x:-moz-broken, x:last-of-type { background-image:url(img/bg04.png); /* Fx 3.5 and newer */}

div.sample, x:x { background-image:url(img/bg00.png); }

FF3.5が嫌いです。