The Silverlight manager is not part of the Default toolbar of RadEditor. This file browser manager is available in older versions of RadEditor but it has never been promoted officially and it has never been part of the default toolbar even in previous versions of the control.
I added the Silverlight tool to the FullSetOfTools toolsfile file, which you can download from here
. I will also add information about this tool to the RadEditor help.
the Telerik team