Then you need to work on your CSS. You need to change the display of your anchor tags to block for this trick to work in Mozilla. Otherwise I think the CSS is pretty straight forward:
a.menu{ color:#ffffff; font-family:verdana; font-size:11px; font-weight:bold; text-decoration:none; line-height: 30px; width:120px; height:30px; position:absolute; background-image: url("up.jpg"); background-repeat: no-repeat; text-align: center; display: block; } a.menu:hover { color:#000000; background-image: url("down.jpg"); }
Nothing too complicated there. You need to set the width and height to the dimensions of the image you are using as a background.
You can view (in an iframe) a working example below: