I have done some experimenting with this new option to post LiveJournal comments on Facebook. What I have learned may calm some troubled souls.
In order to cross-post a comment on Facebook, I have to log in as a Facebook user, not as a LiveJournal user.
While logged in via Facebook, I tried to comment on a friend's friend-locked post. I could not post my comment on LiveJournal, much less on Facebook:
So it would seem your friends-locked posts are safe from the evil Facebook. Pass it on. Please!
By the way, this is what a cross-posted comment looks like over on Facebook. I'm still not quite sure what this cross-posting is good for, but I'm not afraid of it.
Please feel free to link to this post, pass the information on, repost it, try the experiment yourself and report back, comment on here and at Facebook, or whatever.
— Sue Burke