Hover works in Safari, not in Firefox

css hover

[neoplasm]

I can't get the hover to work in Firefox. What am I doing wrong?
This is the code:

.ellipses {

width: 130px;
height: 87px;
font-size: 9pt;
line-height: 7em;
text-align: center;
background-image: url(smallellipse2.png);
background-repeat: no-repeat;

}

.ellipses:hover {
background-image: url(smallellipse2invert.png);

}

Thanks very much.

[surrealillusions]

Whats the html code to go along with the css?