It seems alert dialogs are not handled properly in FF. 

Steps to reproduce:

Execute the attached test.

Expected behavior: Step 6 Handle Alert dialog to pass
Actual Behavior: Step 6 is failing with the following error:

Failure Information: 
~~~~~~~~~~~~~~~
Timed out waiting '20000' msec. for any dialog to be handled '1'
InnerException:
System.TimeoutException: Timed out waiting '20000' msec. for any dialog to be handled '1'
   at ArtOfTest.WebAii.Win32.Dialogs.BaseDialog.WaitUntilAnyHandled(IEnumerable`1 dialogs, Int32 handleCount, Int64 timeoutMilliseconds, Boolean resetHandleCount)
   at ArtOfTest.WebAii.Design.IntrinsicTranslators.Descriptors.DialogHandlerDescriptor.Execute(Browser browser)
   at ArtOfTest.WebAii.Design.IntrinsicTranslators.Descriptors.DialogHandlerDescriptor.Execute(IAutomationHost browser)
   at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.ExecuteStep(Int32 order)

Reproduced with TS version 2012.2.1527