Best extension for privacy ever!
It makes possible to have several identities/account on the same platform.
Also, you can containerize websites which try to connect everything you do.
I wish it was available for Android too, but I understand it would require special UI and need more computing resources.

[to all the people finding it useful but complaining of minor missing features and giving few stars: it's not nice!]

Essencial. Essa extensão auxilia muito na privacidade. Abrir cada tema num container é imprescindível para uma navegação efetivamente privativa. Recomendo.

神了，超好用

Very useful to use several accounts of the same service. Also, to reduce unsolicited tracking.

Still the best

I LOVE this extension. I work at job that has me doing a lot of stuff and being able to separate my work web life from my personal web life is AMAZING! I can be logged into two CMS systems and never have to log out because of containers. It's glorious.

The best extension for Firefox. Not is perfect, but is excellent.

The add-on works well in the background and just shows a decent notification to check the visited website is opened inside the specified container. Good idea - great implementation!

I work in the Software Security field. One of my biggest paranoias is that a rogue site will be able to access one of my protected sites, such as banks or email. In the past, I was able to mitigate this by using different profiles in Chrome, but that required separate browsers to be running. Firefox had profiles, but I couldn't open them simultaneously, which made them useless. Now with Firefox containers, I am opening my email in separate contexts from my shopping, and other contexts. I have separate containers for different roles in trusted platforms. The big win is that I can set defaults for my sites. For instance, Amazon always opens in my shopping container. Sweet.

The only reason I cannot give this five stars is because of this one criticism. Links from my email open by default in the same container as my email. This is a security shortcoming because it opens me up to phishing attacks. You can work around using the context menu and opening in a specific container, but I would rather it be a default.

Very good extension. Please ad this add-on's data to Firefox sync. I'm using Firefox on many OS and it would be greet if i had the same containers.

1-No sync with firefox sync.
2-No Mobile version

Great functionality, avoids the need for having two browsers open for personal stuff, work, banking, shopping etc. The only missing thing is easy hotkey press defined by the user or something like CMD/CTRL+SHIFT+1 to open a tab in the container defined first.

Very useful in separating activities, but needs extra functions (particularly sync) to be optimal.

suggestions:
1- organizing the containers in folders and sub-folders structure: I don't use it as much because I manage many accounts, and it would be nice to have the option to create folders. For example: you would have a folder called "Others accounts" and in it there is two folders "Managed businesses" and "family." Inside "Managed businesses" folder you would have business1, business2 etc.

2- adding description to containers and viewing them when hovering over them

3- have more custom control on colors and icons of containers, let the community make icons which could be added within the add-on

4- domain specific containers, example FACEBOOK.com

5- having two check marks; ☑ Always open this website/URL (Facebook.com) with this container (My Facebook) ☑ Except when I am in a different container.

Meaning if you made a container for a family member Gmail, Facebook, or their Other accounts; For example your mother, father, or technologically illiterate girlfriend accounts then you would be able to protect your privacy on ANY site not just Facebook, and manage other people or your other accounts.


Edit:

6- when long pressed the search bar or the arrow key in the Address bar button you can search or navigate to a site with a specific container

This tool is really helpful, as it helps me use different accounts for different services, without having to login and logout of accounts

As part of my work, I am regularly logging in and out of the same site with different usernames. Because each container holds its cookies separately, I'm able to run multiple instances of the site, which cuts back on my login/logout time and drastically improves my efficiency.

Firefox user for life because of this add-on.

I think there are a couple of additional features that could be added going forward, like default container and switch to container. But so far its brilliant and I get alot of use out of it, between personal and work accounts

very nice extension: it allows to easily manage multiple accounts (I use this to separate my work and home stuff)