"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."

Never that simple is it...

Awesome, it works. Thanks!

Notes:

    first go to facebook.com > arrow in upper right > Settings & Privacy > News Feed Preferences > and scroll the whole list to the bottom
    open your console and run the script, and wait. The script takes 1.5 seconds per each "unfollow", so if you have 500 for example, it will take more than 8 minutes :)