the function

static gboolean
tool_button_press_event_cb (GtkButton *button,
                            GdkEventButton *event,
                            EphyNavigationHistoryAction *action)
{
  if (event->button == 1) {
    [...]
    return FALSE;
  } else if (event->button == 3) {
    [...]
    return TRUE;
  }
}

Triggers compiler warnings which are raised by build root policy enforcement on openSUSE to errors 
I: Program returns random data in a function

The compiler is 'right' as there is plenty of 'room' to reach the end of the function wihtout a return statement...