A1> the marionette client is setup as soon as we call `marionette.client()`, right? Anyway, we don't really care because we restart the app in the test anyway.

A2> we can push prefs and settings using `marionette.client({ settings: { key: value }, prefs: { key: value } });`

So my idea was to have a pref that would control injecting this atom automatically, somewhere in system or in gecko.