I have tried this addon on two of my laptops. Both systems stops responding shortly after installing and remains in hung state for around 20 minutes, then firefox crashes and system comes back to life.
using ubuntu 20.04.
Edit - Now that i have deleted add-on. it is still showing container option in right-click menu!

Одно из самых полезнейших дополнений. Очень удобно для использования одних и тех же сайтов из одного окна.

Cette extension est un compromis parfait entre la sécurité absolue (1 onglet=1 session) et la performance (n onglets = 1 session). Je sépare ainsi mes onglets par groupes: "Personnel", "Professionnel", "Finance", "Transactions", "Google", "Facebook" et "Suspect". Cela me permet, par exemple, de rester connecté à mon compte Google sans rouvrir automatiquement la connexion à chaque redémarrage. Un module indispensable pour moi!

so much better than the Chrome's multiple people feature. Thanks Firefox.

So disappointed that my containers (except the default ones) just randomly disappeared today. It could be because I clicked a button in User-Agent Switcher & Manager which said something along the lines of - use/connect Multi-Account Containers - but now I'm so mad because I have to recreate the containers. My rating (before this incident) is actually 5-stars. They've also made it easier to "Always open this site in..." a container which makes setting up more convenient.

Tab will crash when it is opened in container.

Print > simplify page > print, and tab will crash

Najlepszy!

Thank you for this extension! This extension helps me not to delete cookies and site data when the browser is closed. Though I think there are two points to improve:
1. When a new site is opened, the extension could recommend a container for this site. Will save some time instead of doing things on my own.
2. Be able to delete all the site data only from the "main" space (when no container is in place) when a browser is closed. At the moment, "Delete cookies and site data when Firefox Developer Edition is closed" flag is applied not only on the "main" space, but also drops the data from the containers (which doesn't seem correct to me).

Since Sync feature was introduced for this add-on the container flag no longer comes back with session restore.

When I use containers that were created some time ago, tabs re-open in those containers, correctly.

When I create new containers these tabs open in normal tabs when the session is trestored, so the container flag is lost for them.

Whatever may be the difference between older and newer containers - since the sync feature was added this behaviour is happening, rendering the add-on useless in my case.

This is a nice addon for multi tasking with 3 or 4 Youtube accounts

Molto utile, all'inizio sembra complicato usarla ma poi ci si abitua.