fixed.js

var map = L.mapbox.map('map', 'XXX', {zoomControl: false})
    .setView([-20.1908, -67.5893], 3);

var geoJson = {
    type: 'FeatureCollection',
    features: [

    {
        type: 'Feature',
        geometry: {
            type: 'Point',
            coordinates: [-67.5893, -20.1908]
        },
        properties: {
            title: 'Salar de Uyuni',
            'marker-size': 'small',
            'marker-color': '#fff',
            url: 'http://localhost'
        }
    },

    {
        type: 'Feature',
        geometry: {
            type: 'Point',
            coordinates: [170.2, -43.4764]
        },
        properties: {
            title: 'Franz Josef Glacier',
            'marker-size': 'small',
            'marker-color': '#fff',
            url: 'http://localhost'
        }
    }

        ]
    };
var myLayer = L.mapbox.featureLayer()
  .setGeoJSON(geoJson)
  .addTo(map);
  
myLayer.on('click', function(e) {
    e.layer.unbindPopup();
    window.open(e.layer.feature.properties.url);
});

map.fitBounds(myLayer.getBounds());