Makercluster is loaded from developers.google.com but loading is prevented in Firefox due to privacy settings. **How to fix** - Install [markerclusterer](https://github.com/googlemaps/v3-utility-library/tree/master/markerclusterer) via npm - Import it in [GMap initialization](https://github.com/LIN3S/FrontFoundation/blob/master/src/js/ui/vanilla/components/GMap/init.js#L21) - Change loading strategy for gmap dependency, no need to be async