Version 2010.2.929.35 is very old and it does not support the latest versions of the modern browsers. My suggestion is to test the live demos of RadEditor and if the problem does not exist to upgrade to the latest official build 2012.2.912, which supports all modern browsers.
All the best,
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