Created Unassigned: using BalloonPopupExtender inside TabPanel and browsing in FireFox [27395]

when i use BalloonPopupExtender inside TabPanel, as below:
<ajaxToolkit:TabContainer ID="TabContainer1" runat="server" ActiveTabIndex="1" Height="177px"
Width="436px">
<ajaxToolkit:TabPanel runat="server" HeaderText="TabPanel1" ID="TabPanel1">
<ContentTemplate>
<asp:TextBox ID="MessageTextBox" runat="server" Width="200" autocomplete="off" />
<br />
<br />
<asp:Panel ID="Panel2" runat="server">
This Balloon Popup uses the Cloud style.
</asp:Panel>
<ajaxToolkit:BalloonPopupExtender ID="PopupControlExtender2" runat="server" TargetControlID="MessageTextBox"
BalloonPopupControlID="Panel2" Position="BottomRight" BalloonStyle="Cloud" BalloonSize="Small"
UseShadow="false" DisplayOnClick="true" DisplayOnFocus="true" />
</ContentTemplate>
</ajaxToolkit:TabPanel>
<ajaxToolkit:TabPanel ID="TabPanel2" runat="server" HeaderText="TabPanel2">
<ContentTemplate>
<asp:HyperLink ID="link1" runat="server">Click Here to Show the Balloon Popup</asp:HyperLink>
<br />
<br />
<asp:Panel ID="Panel1" runat="server">
This Balloon Popup appears when you click the link. It uses a Rectangle style and
it is set to appear at the top-right of the link.
</asp:Panel>
<ajaxToolkit:BalloonPopupExtender ID="BalloonPopupExtender1" runat="server" TargetControlID="link1"
BalloonPopupControlID="Panel1" Position="TopRight" BalloonStyle="Rectangle" BalloonSize="Small"
UseShadow="true" />
</ContentTemplate>
</ajaxToolkit:TabPanel>
</ajaxToolkit:TabContainer>

it can display normal in IE but innormal in FireFox the first time.