testEnterNormalizeNodes() {
    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 BR as FF does.
      helper.select('one', 3);
      field1.getElement().focus();
      events.fireKeySequence(field1.getElement(), KeyCodes.ENTER);
      const range = field1.getRange();
      assertTrue(
          'Selection should be in P tag',
          range.getStartNode().nodeType == NodeType.ELEMENT &&
              range.getStartNode().tagName == TagName.P);
      assertTrue(
          'Selection should be at the head and collapsed',
          range.getStartOffset() == 0 && range.isCollapsed());
    }
  }
Regression test for http://b/3051179 . Tests that when you hit enter and it
creates a blank line with a BR and the cursor is placed in P.
Splitting DOM causes to make an empty text node. Then if the cursor is
placed at the text node the cursor is shown at wrong location. Therefore
this test checks that the cursor is not placed at an empty node. Fix is in
a Gecko-only codepath, thus test runs only for Gecko.