I tried these the first time I made them, but it always errors out as

 EXCEPTION: no message!
    at: nonesuch line 0

Hence why I switched to the classic way. I'm comparing to https://github.com/Demelode/thunderbird-ensemble/blob/master/modules/connectors/TBMorkConnector.jsm and I've got it exactly the same way, but it doesn't complete the tests. Any ideas?