This extension is okay but has at least two major issues:

• It's a massive pain to do things that require third-party sites, for example, if you put Google into its own container, logging into StackExchange sites using OAuth or logging into YouTube become quite the ordeal. 😕 Likewise, you can't log into YouTube unless you reassign Google to "always in" YT's container, then log in, then reassign Google back to "always in" its own container. It's a MASSIVE pain! Similarly, if you put eBay in one container and PayPal in another, you won't be able to make purchases anymore because you can't log into PayPal through eBay. 🤦

• Likewise, there's no way to use wildcards or container-ize subdomains, so you have to add them all manually. For example, you can't put ALL StackExchange sites (*.stackechange.com) in a container together, you have to manually visit each one individually, then do the multiple clicks and mouse-movements to set it to open "always in se container". And then, you have to do it ALL OVER AGAIN for each one's meta subdomain. 🤦 Not only is it a massive pain, but it also defeats the point to containers since SE can track you via all the other sites that aren't in a container, including drive-by one-off SE sites you might find yourself on where you don't even have an account. 🤦🤦🤦

• I temporarily disabled the addon to try to debug an issue with a site, and when I re-enabled it, ALL of its settings were gone, all the containers, all the assignments, everything. Worse, restoring the containers from a backup doesn't help because it already WIPED OUT ALL THE COOKIES! 😠 Apparently this has been a bug for a long time and they STILL haven't fixed it. (I guess they're too busy wasting their time integrating Mozilla VPN. 😒)

• It also doesn't seem to work for this site (addons.mozilla.org), I checked the code to see if they put an exception for it (for some reason 🤨), but it doesn't seem to contain one, it just doesn't work. (Maybe Firefox suspiciously treats this site in a different way at a base level. 🤔)

• The interface is extremely lacking. There is no way to directly edit the settings such as a text-box to enter domains to assign containers. The only way to do so is to actually go to a site and then assign it to a container. This has numerous problems:
◦ It allows a site to track you at least once before you assign it to a container.
◦ It doesn't work if you're offline.
◦ It doesn't work if the site redirects to another domain or even subdomains (eg www.), so it can harvest data and quickly redirect, passing the data and preventing you from assigning the original domain to a container. This addon NEEDS a proper UI.