Weave.Service.onStartup now triggers autoconnect after a fixed delay specified in a preference. If that preference is absent, nothing happens and apps are responsible for triggering autoconnect in a weave:service:ready observer themselves. Provide such observers for Firefox and Fennec.
Weave.Service._registerEngines now reads the list of engines from a preference so that apps can specify it this way. The switch logic stays as fallback for the addon case.
