Cambios

var abbrs = {};

$("ul#listwidget-1 li a").each(function (i) {

abbrs[this.firstChild.nodeValue] = this;

});

$("#filtro").on("keyup", function() {

var filterBy = this.value.toLowerCase().trim();

for (var abbr in abbrs) {

if (abbr.indexOf(filterBy) !== -1) {

var li = abbrs[abbr];

// show li

}