Errors without stack information, caught by RemoteAddonParent.jsm, are currently reported as having originated in that file. This is somewhat confusing, and I suspect is going to lead a lot of extension authors not to associate the errors with their code. I certainly did, until I read through that file to figure out what it did. We should make some attempt to report some meaningful source location for errors without that information. The source file/line number of the handler function would be ideal, but the line number where the listener was registered, or some pseudo-URL based on the add-on ID, would be better than the current situation.