Firefox下javascript如何操作剪贴板Clipboard

//Firefox下Clipboard的读写js脚本
//将字符串maintext复制到剪贴板
function setClipboard(maintext) {
   if (window.clipboardData) {
      return (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);
      return true;
   }
   return false;
}

//返回剪贴板的内容
function getClipboard() {
   if (window.clipboardData) {
      return(window.clipboardData.getData('Text'));
   }
   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');
      clip.getData(trans,clip.kGlobalClipboard);
      var str = new Object();
      var len = new Object();
      try {
         trans.getTransferData('text/unicode',str,len);
      }
      catch(error) {
         return null;
      }
      if (str) {
         if (Components.interfaces.nsISupportsWString) str=str.value.QueryInterface(Components.interfaces.nsISupportsWString);
         else if (Components.interfaces.nsISupportsString) str=str.value.QueryInterface(Components.interfaces.nsISupportsString);
         else str = null;
      }
      if (str) {
         return(str.data.substring(0,len.value / 2));
      }
   }
   return null;
}