"Hide and Show" feature is advertised, and I selected and installed the Add-on exactly for this use case. Now I can't find the feature. Can you please point me to it ?
See 2 "discussion" on this page related to the feature. My Conclusion: Falls short of this advertised use-case. Rating down for the time being until the discussion brings a solution to the restrictions.

You can lose your data. Do not trast this add-on! Very raw product.

Good idea in principle, but will only work with my email account for a week or two, then instead of opening container it throws me back to the email log-in screen. If I disable or remove this add-on, all is well.

Does NOT work in private tabs!
I always use private tabs by default, once I installed the extension nothing happens.
I've checked the permissions and there's no way to allow it to work in private mode.

A real shame!

no longer auto opening tabs in the correct container that ive assigned them. not even facebook.

Le raccourci clavier Ctrl + . (point) n'ouvre pas le panneau contextuel.

It doesn't remember your login details and you need to log in every time

I breaks Distrokid's claim YTube artist page, and works weird with Google, it constantly ask if I want open something in other tab which is annoying.

As soon as the extension is deactivated, almost all data is erased! There is no way to recover anything and you cannot make a backup! This makes it INUSABLE. This is a very serious problem that has never been solved!!! Why don't you use Firefox Sync?

Mozilla set big expectations for this extension, but it did not work at all in Firefox 84.0 for Mac. I installed and enabled it, but the add-on's icon never appears in the toolbar and right clicking on web links does not present an option to choose a container. In the manager for the add-on, I created new containers in addition to the defaults and they disappear as soon as I exit the manager and re-enter it. A perpetual warning message appears in Firefox's Preferences indicating "An extension, Firefox Multi-Account Containers, requires Tab Containers," as though they are not enabled and need to be. Yet the checkbox for Enable Tab Containers right below that warning is enabled. So tab containers appear to be enabled, but the add-on is completely non-functional and worthless, and there are no help articles that address the problem of the icon not even showing up and no container-choosing functionality appearing after install. Mozilla set big expectations or this add-on and delivered a big disappointment.

Nothing was shown by site mangers. It's quite unti-user friendly.

Container implies that it holds something. I was hoping that each container would hold one type of website that i often have many open - such as youtube. I want a youtube container that I could throw videos in to watch later. Watched several how to videos for this adon but nothing was said about that. Tried to see if it would work like that. Don't think so.
Better if Firefox called this thing "accounts" or something like that as all I can figure out is that it separates accounts.
Somebody tell me I'm wrong and it works that way the name implies.

When I restore a previous session (that's an official setting in Firefox), the tabs reopen in a non-conainer.
Also, I did not find a way to assign tabs in bulk to a container.
These 2 problems together make the plugin unusable: I am uninstalling.

It only works for a short period of time,then the pop up box, to select the container you want comes up as a blank white box,it happens every time I've loaded it & reloaded it & cleared caches & refreshed firefox & reinstalled all add-ons 1 by 1 & it doesn't matter it always happens & you lose it & all the other mutli acct containers that are based on the same code, so I can't open certain sites now,when the tab is closed I can't go back into container so I can't safely use my social media, thanks, can you fix this shit? asap & I'll change my stars to higher 4 or 5 likely but as it stands I give a 1 star since it's not only unusable it's preventing me from even logging into my social media totally..& safely

очень жаль что невозможно использовать в приватном режиме. Я ВСЕГДА запускаю браузер в приватном режиме и использую мастер пароль для моей безопасности

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!

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.

It was more annoying than anything else. Once I removed it, I had to restart Firefox 3 (three) TIMES to remove it from the context menu. Once should be sufficient. Certainly not twice, and definitely not THREE times.

The latest update ask for permission of 'Exchange messages with programs other than Firefox' and 'Control browser proxy settings', which is ridiculous for people who do not use Mozilla VPN.
It should only be an optional permission!

Cannot save settings for multiple container of a same site. And when I reload, the duplicates will gone or will only use one container.
Which is not what I expected. Well it does what it does but the way it does it makes me think the title is a bit misleading.
Multi-Account container? NO just call it Firefox Web Container please. Or Firefox Multi-Web Container.

why did you remove this functionality in the newest update to Firefox? why are you making the program worse rather than improving it?