I am not sure why the DIV mode does not work for Firefox. The content area is rendered as a standard editable DIV and the links are not touched by the editor.
Could you please test your scenario in an editable DIV
<div contenteditable="true" style="width:300px;height:300px;border: 1px solid red;">sample content</div>?
If the problem is reproducible in it this means that it is browser related.
If the problem is not reproducible in an editable DIV, please provide a live URL to the problematic page, sample content and reliable steps to reproduce the issue.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed