Lost My Search Engine

I don't know how this happened. My firefox running fine as usual but just now when i opened it all the search engine was lost! i tried to restart it but it's still the same.

does anyone know how to restore all the default search engine? Coz the restore default button in manage search engine doesn't work and i can't find any google or yahoo search engine plugins in mozilla addons website.

BTW i'm using firefox 2.0.0.18