Instagram Relations Exporter
This extension let's you view and export (to CSV) lists of users you follow or follow you on Instagram. There's also a special list called "Not Mutual" that shows who you follow and doesn't follow you back. Another interesting feature is the "Ignored" list, where you can specify a username to be ignored from the "Not Mutual" list.
These features are useful for you to manage who you follow, who follows you and find out who unfollowed you.