Modal window has an excessive <li> in the tabs

The modal windows contains this element:
<li>xzczczczcxxz</li>

Which causes it to look like this on Firefox (and potentially other browsers). This prevents the modal from being useful, as the buttons are actually not there.

On chrome it looks like this which is usable but still not perfect (unrelated to the excessive <li>).

Lastly, selected text on Firefox with the source in firebug: here.