Just works, as advertised. I use it to be logged into two different accounts in the same browser :)
The only feature that can seem kinda buggy is the "always open in default" which I understand to mean that new tabs will be opened in the "default" container, this is not the case and I haven't found a consistent pattern.

But that said, it opens links in the same container the source page is in, and it "just works".

One of the most useful add-ons available right now.

The idea is great, it worked great. It took me weeks to finetune everything and really think about what I would like to open in which container. Had a few problems with webshops opening in one container and the bank to pay in a different one. Also quite a few 'prove that you are who you say you are by clicking the link in your email' type of situations, which were opened in the wrong tabs. Everything in the end worked great! But then I had a problem with firefox and decided to refresh firefox. Normally not a problem, due to sync I have all my settings back within a few minutes. But every site was opening without containers. I waited and waited and waited and waited... Yeah, no link to sync. Bye bye weeks of work to get 12 containers work brilliantly.

Since one of the most important functions is completely missing... only 2* otherwise 5*

First: good idea. But there is no such thing as being able to "sort" the container folder. I looked everywhere.
Second, I created new tabs under the provided option, but I do not have or see the option to create a new one when I rightclick to see the container with all tabs there.It does only show "re-open a container. I don't want to reopen but create a new additional one.
I have right no pages in any tab because just installed the multi container addon.
Howand when does the option "to create a new tab" show at all?

Maybe I don't understand the concept. Should it not be able to be handled similar to a bookmark or save the tab?
It's not very clear from the writeup for options.

I don't use Firefox Multi-Account Containers to its full potential, and it's great when I do use it. Wish it existed years ago.
It's going to take some time to focus on creating meaningful containers (and applying them). From there, it should be easy.

It has worked for a short time, you could create tabs with their own container, and it just stopped working, it stopped creating tabs all together. I do not recommend, it is unreliable.

Amazing. Was using two profiles w/o knowing this extension exists. Thanks, Mozilla.

Privacy on the fly!

Wonderful tool for keeping your browsing efforts separated and fenced off from nosy Bots.

Seems like I had to do three things to make reopening in the right container "auto-magic";

Open a new tab in the "Amazon" container (long click on '+'). Past the URL into the new Amazon container tab.
Click the Multi-container symbol and select "Always open in Amazon"
Open a non-container tab and paste the URL, select "Remember my decision to always open in Amazon container"

After all 3 of these steps are done, the URL will always open in the selected container.

Once these 3 steps are done you're all set. However there are currently 2 things missing from this and other "container tools";

1. Easy Export/backup/restore/Import of container rules. It would be lovely if this capability were available in CSV and JSON formats. [Necessary for setup of multiple machines without Sync, and off-site storage of config(s)]

2. An easy way to Edit container rules beyond just delete and start over. This will allow quickly changing custom behavior(s). #1 might take this issue toward "feasible".

I put my own website (with multiple applications) in a container to keep nosy bots out of my site cookie jars.

Great idea, love having this feature. I'm tired of having everything I looked at on Amazon.com show up in my Facebook feed. This is a win for privacy and giving browser experience control back to the user. No other browser appears to have these tools, just Firefox.