Error while using :after pseudoclass in contents.css

[Rike]

1) use ​http://ckeditor.com/demo#full, clear all (I used Gecko - last version of PaleMoon)
2) change contents.css or use different way do add style: .cke_editable span:after {content: ' [' attr(class) ']'}
3) write "blah blah".
4) select line and change Style to marker (now you will see yellow line: blah blah [marker]).
5) go to the end of this line.
6) press left arrow and obtain twice this error:

Error: Permission denied to access property 'nodeType'
Source File: http://cdn.ckeditor.com/4.4.2/standard-all/ckeditor.js
Line: 364

[Piotrek Koszuliński]

FF bug