ごめん、こうか
(function() {
var searchbar = document.getElementById('searchbar');
if (!searchbar) return;
var searchbox = document.getAnonymousElementByAttribute(searchbar, 'anonid', 'searchbar-textbox');
searchbox.addEventListener('keydown', function (e) {
if (e.keyCode != 9) return;
var newIndex = searchbar.engines.indexOf(searchbar.currentEngine);
newIndex += 1;
if (newIndex >= 0 && newIndex < searchbar.engines.length) {
searchbar.currentEngine = searchbar.engines[newIndex];
} else if(newIndex = searchbar.engines.length) {
searchbar.currentEngine = searchbar.engines[0];
}
e.preventDefault();
e.stopPropagation();
}, false);
})();