Ошибка разрыва строки с contenteditable в Firefox

$(document).on('keydown', 'div', function(e) {
  var nl = e.keyCode == 13;
  var shift = e.shiftKey;
  if (nl) {
    var sel, node, offset, text, textBefore, textAfter, range;

    sel = window.getSelection();

    // the node that contains the caret
    node = sel.anchorNode;

    // if ENTER was pressed while the caret was inside the input field

    // prevent the browsers from inserting <div>, <p>, or <br> on their own
    e.preventDefault();

    // the caret position inside the node
    offset = sel.anchorOffset;        

    // insert a '\n' character at that position
    text = node.textContent;
    textBefore = text.slice( 0, offset );
    textAfter = text.slice( offset ) || ' ';
    node.textContent = textBefore + '\n' + textAfter;

    // position the caret after that new-line character
    range = document.createRange();
    range.setStart( node, offset + 1 );
    range.setEnd( node, offset + 1 );

    // update the selection
    sel.removeAllRanges();
    sel.addRange( range );

    // Blur on shift+return
    if (shift) {
      $(this).blur();
    }
  }
});

div[contenteditable] {
	white-space: pre-wrap;
	overflow-wrap: break-word;
}

<script src = "https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div contenteditable = "true">Add line-breaks here</div>