问Firefox扩展正在冻结Firefox，直到请求完成

EN

<statusbarpanel id="eee_label" tooltip="eee_tooltip" 
      onclick="eee.retrieve_rate(event);"/>

retrieve_rate: function(e)
 {
  var ajax = null;
  ajax = new XMLHttpRequest();
  ajax.open('GET', 'http://site.com', false);
  ajax.onload = function()
  {
   if (ajax.status == 200)
   {
    var regexp = /blabla/g;
    var match = regexp.exec(ajax.responseText);
    while (match != null)
    {
     window.dump('Currency: ' + match[1] + ', Rate: '
                          + match[2] + ', Change: ' +  match[3] + "\n");
     if(match[1] == "USD")
      rate_USD = sprintf("%s:%s", match[1], match[2]);
     if(match[1] == "EUR")
      rate_EUR = sprintf("%s:%s", match[1], match[2]);
     if(match[1] == "RUB")
      rate_RUB = sprintf("%s/%s", match[1], match[2]);
     match = regexp.exec(ajax.responseText);
    }

    var rate = document.getElementById('eee_label');
    rate.label = rate_USD + "  " + rate_EUR + "  " + rate_RUB;
   }
   else
   {

   }
  };
  ajax.send();