new window from a window.showModalDialogue() opens another modal window

Question

I have this button which opens up a window.showModalDialogue window. This works smooth n all browsers. The problem is if i have a window.open() inside the page showModalDialogue as a Modal window instead of a independednt window.

/*===========================================*/
/*open window using ShowModalDialogue in page*/
/*===========================================*/

    function modalWin() {
     window.showModalDialog("showModal.htm","name","dialogWidth:555px;dialogHeight:550px");
} 
<INPUT TYPE="button" NAME="newOne" VALUE="Show New Window" onClick="modalWin()">

/*===============================================================*/
/*open window using window.Open in pages opend through modal page*/
/*===============================================================*/


    function openWin() {
 window.open('windowOpen.htm','name1','_blank', 'height=255,width=250,toolbar=no,directories=no,status=no,linemenubar=no,scrollbars=no,resizable=no');
} 

This issue happens only on FIREFOX. in IE it opens as a new window and not a Modal Dialogue window.