I have a photo that received more than 3 likes. It says, "Adam, Bill, Charles, and x others like this".
Based on my notifications, I know that Adam, Bill, and Charles are the friends who most recently liked the photo (Adam being the most recent).
When I hover over "x others", it shows me a list of my friends who liked the photo, also in order of when they liked it.
However, when I click on "x others", the order is different. It's deterministic, but not based on any of the other factors that I would guess - edge weight (unless Facebook's edge weight algorithm is really bad) or date of Facebook account creation.
How is that list sorted?