Is it by design that IP v4.2 screws the start menu internet shortcut when you appy a package & have Firefox set as default web browser?
There is no "HKLM\Software\Clients\StartMenuInternet\Firefox.exe" subtree under Vista. Applying a package adds a skeleton subtree missing vital data which breaks the start menu internet shortcut until you remove the offending subtree with regedit.
This subtree is populated correctly under XP32 SP.
