Privacy Badger is attempting to prevent Facebook from tracking you by blocking URLs known to load tracking code or pixel trackers etc.
This extension isolates your Facebook login cookies while you're browsing on non-Facebook websites, hence making it harder for those tracking techniques to identify you.
How can you load Facebook login cookies from third party websites? I thought they set a cookie on facebook and used that to track you between sites. Third parties add Facebook scripts to their sites that then read the tracking cookie around the web.
Privacy Badger prevents the cookie being sent back to Facebook from these third party websites.
This extension isolates your Facebook login cookies while you're browsing on non-Facebook websites, hence making it harder for those tracking techniques to identify you.