Follcker by Daniel R. Alvarenga

Follcker is a GitHub follower analytics browser extension, working in the ?tab=following tab. There is an interface where you enter your Github user name and a token with the minimum permissions user:read, and user:follow, from this, when you enter the GitHub following page, for each user followed it will be displayed if they follow you or not. It works by calling the github API with your credentials and checking whether a user from the displayed list is also on your follower list.