 ].forEach(feature => {
    async_test(t => {
      var prefixedMessage = new PrefixedMessageTest();
      var featureString = `${featuresPrefix}${feature}`;
      prefixedMessage.onMessage(t.step_func_done((data, e) => {
        e.source.close();
        assert_equals(data.height, baselineDimensions.height, `"${feature} begins with an invalid character and should be ignored"`);
      }));
      var win = window.open(prefixedMessage.url(windowURL) + '&expected_innerHeight=' + baselineDimensions.height, '', 