This Add-on is Excellent, I think it should be embedded on Firefox. I discovered this extension by chance.

Containers is simply amazing for the work that I do. I maintain electronic accounts and services (web, email, domain, etc.) for many different clients. Before containers, I would often need to either log off one account to log on as another, or open several private tabs. Now I keep one container for each client, meaning cookies and session info stay present. Whenever I need to make a change, I simply open that client's container, head to the right service, and everything's already logged on and ready to go. I only wish a) there were more icons to choose from, and b) there was a way to sort container names (not the container tabs, but the container names themselves) in the GUI. But if you handle multiple accounts for the same web sites, this add-on is a godsend.

L'option permettant de lié le site à un conteneur est très pratique.

Must have extension in this day and age.

This one has become a must have. No way I can manage the daily routine without it now.

Helps me visit otherwise privacy intrusive web services.

dùng tiện ích

A very useful extension.

I never knew I needed this until I used it. This is by far the most important (and practical) extension I have come across, especially if you have separate email accounts for work/home/etc.

Finally I can use multiple accounts instead of openning incognito mode or using other browsers.

Sadly, it still does not support right-click from bookmarks bar.

Easy way to sandbox different accounts. The ability to keep personal, work and other sites separate from each-other is awesome.

super pratique!

Now Office 365 using multiple accounts is not painful to manage on a daily basis.

Best thing to happen to Firefox since the Private Tabs addon doesn't work anymore! It's a bit complicated to make the addon learn the domain rules. But it works. Combine it with the addon Cookie AutoDelete! That basically gives you private tabs instead of having to open private windows.

Great extension!

It's so good, it's literally one of the biggest reasons why I use Firefox over Chrome.

Very useful

very good

Traz muita praticidade ao cotidiano!

This is nice. It's very intuitive and easy to set up again even when your entire configuration is lost.

So easy to use! Easy to keep common items together.

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.