My favorit site for icon is Iconomize.com because the icon anda choose automatically installs to your desktop with the shortcut already set. They have the facebook icon here, link Just click to install and it goes right on the desktop.
In fact yes anda can:First anda go in google gambar and type "FACEBOOK ICONS"and save the pic,then anda go and search"www.iconverticons.com",convert the pic into an icon and download it,then go in the desktop: go to"new","shortcut",type:"www.facebook.com",then name it "Facebook",then right click on the shortcut ,go to properties,change icon and choose the one anda converted before,then press APPLY.and then it should come perfect