在ff下会弹出提示的copy

function copyToClipboard(txt) {
      if(window.clipboardData) {
              window.clipboardData.clearData();
              window.clipboardData.setData("Text", txt);
      } else if(navigator.userAgent.indexOf("Opera") != -1) {
           window.location = txt;
      } else if (window.netscape) {
           try {
                netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
           } catch (e) {
                alert("被浏览器拒绝！\n请在浏览器地址栏输入'about:config'并回车\n然后将'signed.applets.codebase_principal_support'设置为'true'");
           }
           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 = txt;
           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);
      }
}