Yep, it's Pocket, and it's enabled by default in desktop Firefox. Normally I ignore most of its recommendations, but this one was too heinous to overlook.
Pocket is awesome btw. Not for recommendations, for saving articles to read in the future. It's supported by Kobo so if you have it, save any long form article with a single click in Firefox, and then when you have time read it in your Kobo. Also works with books published on marxists.org etc. Great stuff.
I do rather like it, but mostly because I use it for lemmygrad fodder, like this article. I'm in the stone age lol. I copy and paste links into the notes app on my Mac...