I think it was more a case that it won't work the way they are written today. If they call the Windows URL APIs or handle the MIME types correctly themselves it should work fine.
I'm also confident that the good people working on Firefox will adress that issue. This could become what ActiveX never was! Or in a worst case become ActiveX all over again.
I think the deciding factor will be if it is possible to get end users to pay attention to the security dialogs and not just click accept/deny like zombies.
- Warning: The application "Paris Hilton pictures" needs permissions to mess up your system - is that okey?
- Hell yes, hit me bro!!
CAS is a suweet thing. If people just learn to use it.