Registry changes possible using signed applets?

Recently I have been learning about signed Java applets. But I didn't
come across any article which listed down the privileges (and
restrictions if any) that come along with signed applets. Also whether
there are any compatibility issues pertaining to different browsers?

The biggest question I have is whether a signed applet (loaded on a
Firefox browser on a Windows platform) can make registry level
changes. Has anyone tried this or have any answer to this?

   

Regards,  

-Aayush