To whom it may concern:

If you used Facebook's search bar feature yesterday and were able to see your "top 5" friends, then there will be a PHP file containing the "o" ranking of every single one of your Facebook friends stored somewhere on your computer.

Please note: this tip applies to anyone whose computer saves temporary internet files.

(1) Open your "Temporary Internet Files" folder. (For example, from Internet Explorer, go to Tools > Internet Options > Settings > View Files.)

(2) Within the folder, look for files last accessed on May 13 around the time you first tested out the Facebook search bar function.

(3) You should be able to find a PHP file called "typeahead_search."

(4) Save this file to another folder and open it with a text editor like Notepad (or the Mac equivalent). You will see that the file contains script for every single one of your friends. (See the script here for an example.). If you search within the file for the name of any of your Facebook friends, you will find their ranking after the letter "o." The five people with the lowest "o" rankings will be the same as your "Facebook 5."

It was part of the autocomplete for the search box. The file the server sent when you clicked on the search box was a big list of Friends and groups (that it used to autocomplete when you type) like this:

{"t":"[Dude's Name]","i":2401357,"u":"http:\/\/www.facebook.com\/profile.php

?id=2401357","o":216,"it":"","n":"Northwestern"}

for me the "o:" value here is 216 for the vast majority of the names,
216 being my total number of friends, but some are lower - lo and
behold people with 0-4 are the five people that show up in the search
box

o's just a ranking thing, like so when you type "a" it uses the o
value to figure out which names should come first, then everything
that's 216 is just in alphabetical order

The only thing that remains is how they computed the o values, I
assume the method was something nefarious. Anyway it's gone now, but I
hope this helps. I'm not affiliated with facebook or anything.