According Wikipedia, "Friends for Sale was a massively multiplayer online business simulation game originally developed by Serious Business, available as an application on the social networking website Facebook."
You can still find some screenshots of the game on Google.
FFS Utility was a Chrome extension as a GreaseMonkey script to enhance the interface of FFS game on Facebook.
Enhancements were perfectly integrated in the webpage. Sadly I did not keep a screenshot of the final rendering on Facebook. 😥
I added statistics, charts, autowork, picture monitoring, rank of pets, shortcut to buy a pet, ... Check to code to discover all the features 😉.
JQuery 👌
Date: around 2010