XBAP applications are designed to run exlusively inside Windows Internet Explorer and no other browser. When you are loading these files in non-IE browsers the mime type is not recognized and so these are just treated as file downloads.
You may search the web for some created plugin for Google Ghrome, otherwise you will need to use IE.
The new WPF demos for the RadControls Q2 2011 Beta will be using ClickOnes, so this problem with the browsers will not remain any more. You will just need to download and install the demos.
All the best,
the Telerik team
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