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);    
          alert("复制成功！")    
     }    

?from http://www.iteye.com/topic/125198