I gave you five start

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-----> CAN BE IMPROVE IT :(
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BUG ---> Why always for a new version of firefox I have to set up the plugin even when I have firefox sync activate.

1. Missing --> Not working for Firefox Focus or Firefox Android you have 366,285 Users for sure many of them use android, and there are no plugin you will be the first . Hit first hit twice ;)
why don t port to firefox focus or firefox android or even better integreated with firefox by default

2. Missing --> Better configuration I recomend containers helper https://addons.mozilla.org/en-US/firefox/addon/containers-helper/

3. Missing --> in every firefox version the multiaccount containers icon it desapear from the menu bar

4. Missing --> containers in sidebars https://addons.mozilla.org/en-US/firefox/addon/container-tabs-sidebar/

5. Missing --> Not working in private mode, containers is great to open the same web ex gmail in two cointeiners in the same browser
so I can read work and house gmail but in priveate multi account container doesn t work

6. Missing ---> Automatically open websites in a dedicated container. Simply add rules to map domain or subdomain to your container.
https://addons.mozilla.org/en-US/firefox/addon/containerise/

7. Missing ---> Temporary container option https://addons.mozilla.org/en-US/firefox/addon/temporary-containers/
8. Missing ---> Option of container proxy https://addons.mozilla.org/en-US/firefox/addon/container-proxy

If you disable this add-on then your customizations to existing containers will be lost and any new container you added later will be deleted.

UPDATE: Firefox just (13/2/20) added the sync functionality in this add-on which let's users sync customizations. Will give 5 stars if they also add the functionality of limiting a container only to assigned site(s).
UPDATE 2: They added the functionality. Giving 5 stars now.

Excelente, al principio hay que ir seleccionando que pagina va con cual contenedor, pero despues de hacerlo es super simple ya que se abre automaticamente en el contenedor.

This is THE best feature of Firefox IMHO

It's easy to use to help organize tabs! The ability to have tabs/websites auto open into their respective containers is great!

Lovely, simple, and effective :D

It takes some time to assign the most frequently visited sites onto the right permanent container, and to rewire muscle memory to open sites as containers. But once over that hump it's a truly amazing and lean add-on!

It helps a lot since I need to change frequently between my personal and work Google accounts. I won't need to open different browsers any more.
Just a small bug that when I chose to open the links in my Gmail, this add-on would somehow change the original redirect link and get me to the wrong page.