what determines the order of facebook chat?

[Illigi]

it's always switching on me.. i use to just have the people i talked to most at the top, now all these randoms are there as well. why does it change like that?

[Drizzy]

Facebook has somehow messed up the chat, so it's all scrambled. People that are on the top on the sidebar is the people that you've interacted with the most, like chatting allot and they peek at your facebook page, but now it's all messed up. Mine switches allot too