>>737
これでよろしいかと
(function() {
var searchbar = document.getElementById("searchbar");
if (searchbar) {
  searchbar.handleSearchCommand_org = searchbar.handleSearchCommand;
  searchbar.handleSearchCommand = function(aEvent) {
    searchbar.handleSearchCommand_org(aEvent);
    // clear searchbar
    this._textbox.value = "";
    this._textbox._displayCurrentEngine();
    // reset to default engine
    setTimeout(function() {
      var ss = Cc['@mozilla.org/browser/search-service;1'].getService(Ci.nsIBrowserSearchService);
      ss.currentEngine = ss.defaultEngine;
    }, 0);
  }
}
})();