יהושע בן פרחיה אומר עשה לך רב וקנה לך חבר והוי דן את כל האדם לכף זכות
Y'hoshua ben Prachya says: Make yourself much and buy yourself a friend; and be judging everyone toward the scalepan of merit.
"Buy yourself a friend" means that you should only be friends with someone on a social-networking site for which you pay a membership fee. In fact, since he says you should first "make yourself much", the membership must be expensive. Since Facebook does not (yet) have paid membership available, it is inappropriate to become Facebook friends with anyone.
You might think that you should therefore look down upon someone who tries to become Facebook friends with you; hence the end of the statement, "be judging everyone toward the scalepan of merit".
As always, consult your rabbi for practical halacha rather than relying on what you read on this site.