For Silverlight 4 Application in Firefox, Coded UI test is only supported in Firefox 3.5 and 3.6. For higher version of Firefox, it is not supported.
For Silverlight Application in Chrome, Coded UI test is not supported.
For Silverlight Application in Safari, Silverlight is never supported on Windows platform. It is only supported on Mac OS. However, Coded UI test is not supported for Safari.
As a SDET, I would like to say this is not good news for Coded UI test because it has the huge limitation for Silverlight Application and cross browser testing.
Telerik Test Studio can handle Silverlight 5 Application in different browser easily.