Facebook has an ingrained algorithm that keeps an eye on exactly how you connect with your friends and then sorts as necessary. Resource
Facebook Timeline Friends List Order Meaning
While the specific ranking algorithm is secret, it does think about the following variables:
* Just how commonly you visit your friends' accounts
* Exactly how typically you click on your friends' links
* Photos/tags in common
* Usual groups/ organizations
* utual Friends
* How commonly you search for friends
* Relative appeal (exactly how popular your friends are among your mutual links).
So, the actual sorting is not random, however instead very carefully crafted to facilitate interaction and site engagements.
