def _to_reader_frame(self):
    """Navigate to the KindleReader iframe."""

    reader_frame = 'KindleReaderIFrame'
    frame_loaded = lambda br: br.find_elements_by_id(reader_frame)
    self._wait().until(frame_loaded)

    self.switch_to.frame(reader_frame)  # pylint: disable=no-member

    reader_loaded = lambda br: br.find_elements_by_id('kindleReader_header')
    self._wait().until(reader_loaded)
Navigate to the KindleReader iframe.