I like this! It'd be nice if we could abstract it from email. Perhaps we could put this function in https://github.com/mozilla-b2g/marionette-helper as MarionetteHelper#debug. Then if I am the Calendar app, I could do

    var client = marionette.client();
    client.helper.debug(Calendar.prototype);
    var app = new Calendar(client);
    ...

Thoughts?