PithHelmet is a shareware ad blocking plugin. It works fine with Safari. You must quit safari/webkit to install, but when you try to reopen webkit, it immediately shows an error message. I have contacted the developer and he doesn't know much about webkit, and doesn't plan on making the program compatible. You can contact him here if you need to: Mike Solomon <mike-web@culater.net>. Be nice, he doesn't want any spam.
PithHelmet (and similar software like SafariStand and Saft) rely on internal APIs that don't change. WebKit has changed quite a bit since Tiger (Mac OS X 10.4.x), so crashes are not unlikely. Mike will have to update PithHelmet to make it work again; there's really no other way to fix this. Thus, closing this bug as RESOLVED/INVALID.