An overview of Containers for add-on developers

Containers work by giving users the ability to place barriers on the flow of data across sites by isolating cookies, indexedDB, localStorage, and caches within discrete browsing contexts. This in-depth introduction to Containers and Container extensions explores the capabilities of Containers and contextual identity for developers.

Link: https://hacks.mozilla.org/2017/10/containers-for-add-on-developers/