You could use something like Omnivore for this (it's what I use), is free and open-source and have apps for iOS and Android
It needs Firefox Beta or Nighty to be installed, right?
Yep, that's right. You need to create a collection on addons.mozilla.org and go to Firefox Beta/Nightly settings and there, go to "About Firefox", then you must click multiple times on the Firefox icon to activate debug mode, and now you will have enabled the "Custom Add-ons collection" option where you must enter your username and the collection name to install the add-ons in the collections like any other extension.
Annoyingly, Pocket requires a separate install on android, but it's built in on desktop and is able to do this.
I also use OneTab for this kind of functionality, it let's me save all the tabs or specific ones to go through later.
Just as a side note -- if the user is ok with (or actually prefers) handling the archival & indexing of the material himself/herself, SingleFile works great as a 'read later' tool. It can save into a WebDAV share; can be imported into a self-baked minimal webextension as a library; & has an almost feature-complete mv3 port.
Works on Fennec (based on FFox Beta, I think) though a bit slow, unfortunately. Available otherwise on desktop FFox & Chromium.
Firefox
A place to discuss the news and latest developments on the open-source browser Firefox