I'd much rather they figured out how to fix their sync service - or at least let me actually delete everything on it and start again! I still get temporary containers coming back months after I have deleted them!
I lived through the firefox extension debacle in 2019 or so when FF accidentally let a cert expire and it helpfully uninstalled all my "unverified" extensions, of which container tabs was one. When everything was fixed, my settings were erased.
Except they weren't. To this day, I still get random ghost-like behaviour from my old container tabs settings. Google-contained apps will try to open in my banking container, as I gradually realise all of my containers were deleted but the URL-to-container mapping wasn't, and it was by ID not name, and the IDs have been reused.
Containers should be a core feature because they are /the/ feature ff has over the chrome army right now. I know they were (are?) trying to prove that core features aren't necessary because you can write anything in a web extension (IIRC that's how they justified getting rid of RSS), but it just hasn't been so in my experience.
For mosts it should be easier and more intuitive to use Firefox with First Party Isolation enabled.
The mental gymnastics of container management becomes superfluous, and there is minimal risk of leaking data by mistake.
Not many people use any extensions[1], which is why it should not be an extension, even if it is actually an extension in terms of implementation. Certainly I wouldn't expect my parents to discover and install the extension, but I might expect them to be able to be taught to use a first-class feature.
[1]: As the Firefox base dwindles further to only a hard core of techies, this might not be true, but it's probably true of Chrome: only 13 extensions have over 10 million installs and Chrome is used by over 2 billion people.
Multi-Account Containers
Temporary Containers
Sidebery
The UX for using containers is abysmal, so no fucking wonder. This is the problem with "data-driven" design, it falls for the McNamara Fallacy. It's an over-reliance on 'scientific and objective' quantitative metrics while aggressively ignoring qualitative considerations and analysis. You'll never achieve excellence like this.
Temporary account containers: automatically makes a new tab isolated from the others. This reduces the data thieves tracking and it allows you to ignore sites that have a limit on the number of articles you read before putting up the paywall. For some sites, there is advantage in using the same container so I use Multi-Account containers.
Multi-Account containers: I have multiple webmail accounts and have a container for each one pinned in my main browser window. For me, these containers are aligned with different businesses that I run and personal stuff. Using them is so easy - right click on a tab and reopen in X container.
Containers (and uBlock and side tabs) should be baked into the browser.