Disappearing Bookmarks, and address book ...

[kap]

The FireFox's bookmarks; ThunderBird's address book, email settings and saved messages disappear every time my uncle shuts down his computer hence closes out those apps. Can it be a virus?

This only happens on his business Dell Latitude laptop running XP Home Edition. Everything is working fine on his G3 Mac

TiA

[ho'ard]

Is this after upgrading his Dell to Leopard, by chance?