Hi. To register application for some mime type, it need to add MimeType property to its desktop file. As SailfishOS allows just one instance of application at the time, it should also register D-Bus service and set proper D-Bus options in desktop file… Then expose corresponding methods… I added support for geo: url to OSMScout recently in this commit: https://github.com/Karry/osmscout-sailfish/commit/c49d12641f9d9f654132f436eec1c218e693da9c
Unfortunately, this registration is not allowed in Jolla’s Harbour.