Rather than cfx's --updateurl command, with jpm, we can simply place the updateURL in package.json. This URL points to a file called update.rdf, which tells self-hosted addons where to look for updates.
With cfx, that update.rdf file could be generated with the --updatelink, but that option has been removed from jpm. I can't figure out how to generate update.rdf using jpm. Any ideas?
I've made issue 288 for this, in the meantime you will need to follow these instructions to learn how to build the update.rdf yourself https://developer.mozilla.org/en-US/docs/Extension_Versioning,_Update_and_Compatibility#Update_RDF_Format