Marionette does not listen for onDOMContentLoad events when navigating backwards, forwards, or refreshing. This is causing tests that use these API calls to be flaky.
The underlying issue here is that the pages are getting loaded from bfcache. So as you noticed we do not see those page events.
This also happens for Element Click.
geckodriver tracking issue: https://github.com/mozilla/geckodriver/issues/308