bool mouseLocked = false;
// Tell the widget if mouse lock is on
if (aEvent->widget) {
  nsIFocusManager* fm = nsFocusManager::GetFocusManager();
  if (fm) {
    nsCOMPtr<nsIDOMWindow> currentWindow;
    fm->GetFocusedWindow(getter_AddRefs(currentWindow));
    if (currentWindow) {
      nsCOMPtr<nsIDOMNavigator> navigator;
      currentWindow->GetNavigator(getter_AddRefs(navigator));
      if (navigator) {
        nsCOMPtr<nsIDOMMouseLockable> lockable;
        navigator->GetPointer(getter_AddRefs(lockable));
        if (lockable) {
          lockable->Islocked(&mouseLocked);
          aEvent->widget->mMouseLock = mouseLocked;
        }
      }
    }
  }
}

// Remember the previous event's refPoint so we can calculate movement deltas.
if (mouseLocked && aEvent->widget) {
  nsIntRect bounds;
  aEvent->widget->GetScreenBounds(bounds);
  aEvent->lastRefPoint = nsIntPoint(bounds.width/2, bounds.height/2);
} else {
  aEvent->lastRefPoint = nsIntPoint(sLastRefPoint.x, sLastRefPoint.y);
}