Popup dialog behind ASP.NET AJAX ModalPopup in FireFox

Here is how my page is structured.
1. User sees a GridView with an "Edit" button at the beginning of each row.
2. Click "Edit" button will fire an AJAX ModalPopup that contains a DetailsView with the detailed information of the selected row.
3. There is an FCKEditor in the DetailsView.

Now, the problem is that in FireFox, when I click the "Link" icon to add a hyperlink, the popup dialog window is behind the AJAX ModalPopup; however, everything is fine with IE. I have tried to change fckconfig.js file as follows:
FCKConfig.FloatingPanelsZIndex = 2147483648 ;
But it doesn't work.
Can anyone help?

Thank you,