Are you able to reproduce the problem with the latest build of RadEditor? You can test for example the Default Example
of RadEditor. If the problem is still reproducible, please provide detailed steps and content which will help us to reproduce it on our side.
If it is not reproducible please upgrade to the latest build, because version 2009.1.527 is released before the official release of FF 3.6 and does not support it.
If the problem is reproducible in your project with the latest version 2011.2.712, please isolate it in a simple project and send it for examination via a support ticket.
the Telerik team