You can browse the maps of the "repository" via openstreetmap.org in your browser. There are multiple apps using the "repository", like Gnome Maps for Linux or OsmAnd on Android.... And many other apps: https://wiki.openstreetmap.org/wiki/Software/Desktop
What exactly is the problem?
Adding support? It's a web site. If it works on one OS, it should work on the others automatically with few exceptions. Otherwise, it's probably a bug in Firefox.