Please, see the following video: http://screencast.com/t/1E5z4vwd
You will notice that in IE9 it is possible to put the cursor outside and after the table by pressing the right arrow key.
In Firefox this is not offered by the browser and you can workaround it by inserting a simple entity manually in HTML mode or by pasting it along with the TABLE HTML in the OnClientPasteHtml event
All the best,
the Telerik team