Indeed, it is not wise to run third-party bookmarklets while logged into Facebook. This one may be benign, but the next one may not be. If you want to see the JSON we're talking about, just load
Nevermind, I misinterpreted. I just realized it's supposed to be "viewer=[ID]", I was interpreting it as "viewer=[ID]&userid=[ID]". I'm still getting errors, but presumably that's another matter.
https://www.facebook.com/ajax/typeahead/search/first_degree....
with 'userid' replaced with your numeric Facebook account ID.