I think, especially for FireFox, clipboard operations are not something that the UltraWebGrid can control internally. FireFox is very strict when it comes to permissions and especially clipboard operations.

Still, there are some venues you can try. I think the following thread is especially useful:

http://www.experts-exchange.com/Programming/Languages/Scripting/JavaScript/Q_21269346.html

[scroll down a lot after the Ads to see the response]

and especially the generic copy function here:

function copy_clip(maintext)
{

 if (window.clipboardData)
   {
  
   // the IE-manier
   window.clipboardData.setData("Text", maintext);
  
   }
   else if (window.netscape)
   {
  
   netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
  

   var clip = Components.classes['@mozilla.org/widget/clipboard;1'].createInstance(Components.interfaces.nsIClipboard);
   if (!clip) return;
  

   var trans = Components.classes['@mozilla.org/widget/transferable;1'].createInstance(Components.interfaces.nsITransferable);
   if (!trans) return;
  

   trans.addDataFlavor('text/unicode');
  

   var str = new Object();
   var len = new Object();
  
   var str = Components.classes["@mozilla.org/supports-string;1"].createInstance(Components.interfaces.nsISupportsString);
  
   var copytext=maintext;
  
   str.data=copytext;
  
   trans.setTransferData("text/unicode",str,copytext.length*2);
  
   var clipid=Components.interfaces.nsIClipboard;
  
   if (!clip) return false;
  
   clip.setData(trans,null,clipid.kGlobalClipboard);
  
   }
   alert("Following info was copied to your clipboard:\n\n" + maintext);
   return false;
}
//-->

At a first glance, this looks like a permissions problem.  It looks like the browser isn't permitting access to the clipboard.

What version of FireFox?