You've already been hammered with the privacy benefits and yada yada.
So I'd like to outline another major benefit: being able to authenticate to the same service with two different set of credentials. (i.e. logging into the hosting provider with both my personal account and the company's)

At the time of writing this is not working with Sync and there is a lengthy discussion on Github about the challenges of that.
Why it would certainly be nice to synchronize it's still useful as it is.

I work as a web developer on the OutSystems platform and use FireFox all day long for testing, inspecting and debugging HTML, CSS and Javascript code. In my opinion is the best web browser out there :)
Until I knew the multi-account containers extension, I had to constantly login and logout while testing web apps under several profiles. Now, with this extension, I can be logged in under several usernames (each with its own session) on the same browser window and it has made my work soooo much easier!
Thank you very much for your fantastic work on this extension!!!

Indispensable dans un environnement multi-utilisateurs ou dans un contexte de test isolé.
Essential in a multi-users environment or in a isolated testing context.

No hay nada más util, tiene la opción de filtrar sitios para que siempre se habran en un contenedor especifico y es lo mejor

With "Firefox Multi-Account Containers" , I can have multiple gmail accounts in different tabs at the same time. I found this to be very useful. Thanks to brilliant brains behind this!

Very useful, specially for the developers.

Works well. Allows me to open the same website with different identities which is really helpful at work. Thanks!

Super easy to use, only two clicks to open another account.

Pretty cool! HELPS ME A LOT!

Gutes Addon um da Tracking ein bisschen einzuschränken.

einfach zu bedienen, funktioniert zuverlässig

Muy útil, la verdad fué la razón por la que migré a firefox a parte de su rendimiento

One of the best Firefox Add-ons, great for keeping data collecting/hoarding websites and services in check. I'm looking at you Facebook!

It's easy to use and it helps your privacy.
It's also useful if you need to work in multiple environments!

Very useful in web development!

c'est top!

amazing way for abstraction an privacy

Loving it!

Real handy to compartmentalise your different accounts and limit the all-tracking eyes of certain corporations