CalendarExtender in Firefox

Trying to narrow my issue I am having with a ModalPopupExtender in Firefox, so I have deleted everything off of the Panel I am extending and adding things back on at a time. The first issue I have encounted is with my initial CalendarExtender. The Entender opens, but the days are not able to be selected. Cursor stays as a pointer, and clicking on them does nothing. Anybody have any thoughts on what might cause this? Issues is only in Firefox, works ok in IE and Chrome.

<style type="text/css">
        .modalBackground {
            background-color: Gray;
            filter: alpha(opacity=50);
            opacity: 0.7;
        }

        .pnlBackGround {
            position: fixed;
            background-color: White;
            border: solid 3px black;
        }</style>

<asp:Panel ID="pnlModalPopup" CssClass="pnlBackGround" runat="server" Width="325px" Height="275px"><asp:Label ID="Label3" runat="server" Text="Schedule Audit" Font-Bold="True" Font-Size="Large"></asp:Label><br /><asp:Label ID="Label4" runat="server" Text="Schedule Date:" Width="125px" Font-Size="Medium"></asp:Label><asp:TextBox ID="txtCalendar" Font-Size="Medium" runat="server"></asp:TextBox><asp:CalendarExtender ID="cext" Animated="true" TargetControlID="txtCalendar" runat="server" /><br /><asp:Button ID="btnOK" runat="server" Text="OK" UseSubmitBehavior="False" /><asp:Button ID="btnCancel" runat="server" Text="Cancel" UseSubmitBehavior="False" />                                                </asp:Panel><asp:ModalPopupExtender ID="MPE" runat="server"
                                        TargetControlID="btnSchedule"
                                        PopupControlID="pnlModalPopup"
                                        BackgroundCssClass="modalBackground"
                                        DropShadow="true"
                                        OkControlID="btnOK"
                                        CancelControlID="btnCancel"></asp:ModalPopupExtender>