This is right but if u press enter and you have already selected an item this will select the first.
So use this code:
function selectFirstResult() {
infowindow.close();
if ( $('.pac-selected').length < 0){ // this line
var firstResult = $(".pac-container .pac-item:first").text();
var geocoder = new google.maps.Geocoder();
geocoder.geocode({"address":firstResult }, function(results, status) {
if (status == google.maps.GeocoderStatus.OK) {
var lat = results[0].geometry.location.lat(),
lng = results[0].geometry.location.lng(),
placeName = results[0].address_components[0].long_name,
latlng = new google.maps.LatLng(lat, lng);
moveMarker(placeName, latlng);
$("input").val(firstResult);
}
});
}
}