Selection Field content is broken in firefox when clicked on left , right justification plugins.

[pom_ckeditor]

Steps to reproduce:

1.Click on Selection Field plugin and add some values. 2.After adding the content to the editor, select the 'selection field' click on the 'right align'.

3. You will observe that the Selection Field is broken.

Note: This happens in firefox.

[Jakub Ś]

1. Open ajax sample
2. Click on "Selection Filed" button and set values as showed in settings.png
3. Click ok to add select filed to WYSIWG area
4. Click on elements in selection filed and press "Align right" or "Text direction from right to left"

Result: One extra empty selection box created and some values form selection filed are now present in WYSIWYG area (see result.png)

JS error is also thrown:
For "Align right"
Message: startNode.getFirst() is null
Line: 163
URI: /3.6.2/ckeditor/_source/core/dom/range.js

For "Text direction from right to left"
Message: startNode.getFirst() is null
Line: 19
URI: /3.6.2/ckeditor/_source/plugins/justify/plugin.js