Need help on access the editor from a popup window

I was trying to use a popup window to add some data to FCK editor, the only problem is that it only work on IE.

I found the tutorial on FCK docs, anyone knows any alternative mode for

<script language="javascript">
<!--
var variable = null;
var FCK = window.opener.FCK;
  function ok() {
       if(variable != null) {
       FCK.Focus();
       var B = FCK.EditorDocument.selection.createRange(); //only works in IE
       B.text = variable;
 }
window.close();
}
//-->
</script>

That works on Firefox? Thanks