I owe you an apology. When using Firefox, It is not possible to get the text out of an Alert dialog box. The fundamental technical problem is that Mozilla decided to implement their own version of "windows" and text drawing. The dialog and its text content cannot be accessed with the standard Win32 API, which is what we use for the other browsers.
You can see what I mean by using Spy++ (which comes with Visual Studio) to view the window hierarchy of IE compared to Mozilla. I've attached screen shots to demonstrate the difference. As you can see, the Mozilla Alert dialog just isn't visible to Windows at all. As a result we don't have a way of getting at the text content.
I've logged a feature request on this here. Unfortunately there's no way we can get to this in the next 5 months.
the Telerik team
Check out Telerik Trainer
, the state of the art learning tool for Telerik products.