See comments section for more up-to-date versions of the script. The original script is from 2014 and will not work as is.
- Open news feed preferences on your Facebook menu (browser)
- Click people or pages
- Scroll down (or click see more) until your full list is loaded
- Run the script in your browser console
Facebook will block this feature for you while you use it, depending on how much entities you try to unfollow. It automatically unblocks in a couple of hours and you will be able to continue.
I am trying to find a solution. In my case I have 8k in a row and the only solution is to go to the friends>followed section and manually unfollow by hovering over the profile. I will look for a solution to create a method where it does it automatically.