It's been there just as long, turn it on with "privacy.userContext.ui.enabled" and manage them at "about:preferences#containers" The addons added extra functio

It's been there just as long, turn it on with "privacy.userContext.ui.enabled" and manage them at "about:preferences#containers" The addons added extra functionality but everything they've listed in this announcement is already there. Sounds like they're just flipping these two flags by default.