facebook has a few spooks working there (or upstream from there) that try to poison DNS by creating bogus facebook DNS registries. You can get rid of it by deleting your browsers DNS cache.
on most browsers you can type this -
chrome://net-internals/#dns
(replace chrome with whatever browser it is)
then click "clear host cache"
if you're using firefox its
about:networking#dns
and then "clear dns cache"
keep doing it until it goes away, usually once or twice.