OpenStreetBrowser is built from a bunch of modules (e.g. LeafletJS, TurfJS, ...; see the full list) - as most current web applications are. A few of them are written by me (e.g. overpass-layer). And one of them - overpass-frontend - has just gotten more intelligent. overpass-frontend runs in the browser and is responsible for loading map features from an Overpass API (that's a database which has been written specifically for OpenStreetMap data). Before the update, overpass-frontend would already cache map features in the the browser's memory, but it would not know, that a map feature would also appear in a different category. Now, using a in-memory database called LokiJS, overpass-frontend does exactly that. When browsing through many categories, you will notice that already known map features will appear almost instantly. If you think about using overpass-frontend yourself (e.g. in combination with overpass-layer), you might be interested to know, that overpass-frontend can even load a static .osm, .osm.bz2 or OSM .json file and use this as database. Of course, this is only feasible for small amounts of data.