There are still a few things that don't open with microB although they are covered by xrefs and user-mimetype.list. If I try to open an uncompressed postscript file (application/postscript) from the web, microB only offers to save it and doesn't offer dbus-switchboard. Correspondingly, when it's a local postscript file, it just doesn't do anything with it but just says that this type is not supported.

More generally, how can I now tell microB that there is a handler available through dbus-switchboard?