Both my friend and I have Facebook chat activated, and we can both see other Facebook friends listed as online in Facebook chat.
We can't see each other as online in Facebook chat. We've refreshed the page without change. This occurs in more than one browser. She is not in a limited profile list. I've added her to another list which people I can see are in, without change.
There is a search field at the bottom of Facebook chat (at bottom right).
I searched for her using this search field, and the search returned her in the search results, appearing as online.
We have never chat before, but there are also other friends appearing as online in FB chat I don't think I have chat with before. Perhaps I was friends with them before FB changed the visibility settings for chat?