FireFox浏览器复制到剪贴板功能的javascript源代码

根据浏览器复制到剪贴板的功能，具体代码如下：
var txt="要复制到剪贴板的内容";
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("你使用的FF浏览器,复制功能被浏览器拒绝！\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');
     &nb