In EventListenerManager, EnableDevice / DisableDevice need to be called once for each added/removed event listener (if it matches a certain list of event types).
nsGlobalWindowInner::EnableDeviceSensor counts the numbers of calls and expects them to be properly balanced.

EventListenerManager does this correctly for calls to AddEventListener / RemoveEventListener and SetHandler.

But for "once" listeners, we only call DisableDevice if we have no remaining listeners of that type. I'm pretty sure this is wrong - we need to call it once per removed "once" listener.

https://searchfox.org/mozilla-central/rev/bf272a7be6fef0e91bde01dfe1f68403d8fbc237/dom/events/EventListenerManager.cpp#1498-1513

if (IsDeviceType(aEvent->mMessage)) {
  // This is a device-type event, we need to check whether we can
  // disable device after removing the once listeners.
  const auto [begin, end] = mListeners.NonObservingRange();
  const bool hasAnyListener =
      std::any_of(begin, end, [aEvent](const Listener& listenerRef) {
        const Listener* listener = &listenerRef;
        return EVENT_TYPE_EQUALS(listener, aEvent->mMessage,
                                 aEvent->mSpecifiedEventType,
                                 /* all events */ false);
      });

  if (!hasAnyListener) {
    DisableDevice(aEvent->mMessage);
  }
}

The impact of this is that we may waste some power under certain conditions, by listening for device orientation / proximity / light changes unnecessarily.

The patches in bug 1834370 fix this.