JQuery Datepicker Only Works In IE8 (no Firefox, No Chrome For Me)?

Ok so I'm not very familiar with Jquery as to know the possible cause of this, but I've been assigned to find out why the datepicker doesn't work porperly on a client's computer (it prints out the date without slashes like this: 24112008

So when I test the webform, I see it doesnt even pop up in Firefox (the client's browser too) nor chrome, only in IE8.

In the scriptManager we have:

<script src="http://www.website.com/Script/jquery.min.js" type="text/javascript"></script>
<script src="http://www.website.com/Script/jquery-ui.min.js" type="text/javascript"></script>
<script src="http://www.website.com/Script/jquery-ui-i18n.min.js" type="text/javascript"></script>

and in the webform:

$(function pageLoad(sender, args) {
// Datepicker
$.datepicker.setDefaults($.extend({ showMonthAfterYear: false }, $.datepicker.regional['']));
$(".dates").datepicker($.datepicker.regional['es']);
});

The textbox that uses it goes like this:

<asp:TextBox ID="txtFeNac" CssClass="dates" style="margin-left: 7px" runat="server" ></asp:TextBox>