ul.bootstrap-autocomplete.dropdown-menu{
    max-height: 300px;
    overflow-y: scroll;
    -ms-overflow-y: scroll;
    -webkit-webkit-overflow-scrolling: auto;
    -moz-webkit-overflow-scrolling: auto;
    -ms-webkit-overflow-scrolling: auto;
    -o-webkit-overflow-scrolling: auto;
    -khtml-webkit-overflow-scrolling: auto;
    webkit-overflow-scrolling: auto;
}