hello this functionality is part of the pocket ("read it later") extension & will add the open tabs to your reading list...

I do not understand how Pocket works. F ex I have accidentally pressed the Mark as Read and thought it would be found in Archive. It is not there ! You have this option in the Archive too - what does it do ? I have sent these question to support Pocket and got a default response to "We have received your email, and will do our best to answer it as soon as we can" but they never give you an answer. So using Pocket since seems buggy ??