testEnterCreatesBlankLine() {
    if (userAgent.GECKO) {
      field1.setSafeHtml(
          false, SafeHtml.create('p', {}, ['one ', SafeHtml.BR]));
      const helper = new TestHelper(field1.getElement());
      // Place caret after 'one' but keeping a space and a BR as FF does.
      helper.select('one ', 3);
      field1.getElement().focus();
      events.fireKeySequence(field1.getElement(), KeyCodes.ENTER);
      const range = field1.getRange();
      assertFalse(
          'Selection should not be in BR tag',
          range.getStartNode().nodeType == NodeType.ELEMENT &&
              range.getStartNode().tagName == TagName.BR);
      assertEquals(
          'Selection should be in text node to avoid creating adjacent' +
              ' text nodes',
          NodeType.TEXT, range.getStartNode().nodeType);
      const rangeStartNode = Range.createFromNodeContents(range.getStartNode());
      assertHTMLEquals(
          'The value of selected text node should be replaced with' +
              '&nbsp;',
          '&nbsp;', rangeStartNode.getHtmlFragment());
    }
  }
Regression test for http://b/1991234 . Tests that when you hit enter and it
creates a blank line with whitespace and a BR, the cursor is placed in the
whitespace text node instead of the BR, otherwise continuing to type will
create adjacent text nodes, which causes browsers to mess up some
execcommands. Fix is in a Gecko-only codepath, thus test runs only for
Gecko. A full test for the entire sequence that reproed the bug is in
javascript/apps/editor/tests/ponenter_robot.html .