[danShumway]

> That was exactly my point; you're using Firefox's containers for privacy, and it actually doesn't help, at least since they deployed "Total Cookie Protection" by default:

It does. Total cookie protection isolates per-site. What containers allow is for you to say, open a single review site in two different containers, and click on an Amazon link on that review site and not have the same Amazon cookies shared when you do so. It also allows you to very easily set per-site clearing settings for those 3rd-party cookies rather than relying on more cumbersome browser settings.

Total cookie isolation is a great feature but it's a very passive feature with very defined boundaries. Yes, your FB tracking cookies get isolated to the 3rd-party site requesting them. But when do those cookies get cleared, how do they get shared when browsing the same site? It's not just about saying "I want multiple Facbook logins at the same time", it's also about saying "I want this browsing session to be isolated even if I'm revisiting a site that has 1st-party cookies set, even if I'm loading 3rd-party cookies via a domain I've already visited."

By the logic you're supposing, private browsing windows themselves didn't have a purpose after total cookie protection was launched. But being able to fully segment site data by an arbitrary boundary beyond just domain boundaries is useful, and being able to set custom rules including (as this extension demonstrates) even custom proxy rules for how data within that boundary gets treated is even more useful.