Firefox containers aren't meant to be a substitute for profiles, they're a middle layer of security between profiles and private windows. This is exactly what GP was talking about with "layers" of isolation.
Firefox also supports profiles; they have the same isolation as Chrome profiles with the added benefit that they can be stored anywhere on your harddrive, meaning that you can even encrypt a Firefox profile on an external drive and have your history/settings only loaded when that drive is mounted and unencrypted. I will agree that the UI could be a bit better (switching between profiles is cumbersome), but it's a somewhat minor complaint in the same vein as my complaint that containers require an extension to be user-accessible.
Firefox containers are for when you do want to share history/settings, particularly privacy extensions and browser settings, but you want to isolate data between tabs in a way that goes beyond total cookie protection (funnily enough also a feature that Chrome doesn't support) -- containers allow you to isolate cookies between multiple "instances" of the same site, set rules for when site information should be cleared, and they allow extensions to hook into that API in a way that cookie containers don't (to the best of my knowledge) support.
I'm not saying that I wouldn't like having the option to isolate more data with containers (extension settings would be welcome), but that's not really an issue with containers as much as it's just that I'd like Firefox to go even further with offering more granularity. It's annoying to make a profile and need to synchronize settings and extensions from my previous profiles.
> Chrome's extensions in general still have superior security (e.g., activate on click or only for certain websites), so sometimes different profiles aren't even needed.
I also want to throw out a quick objection here: Firefox supports Manifest V3 (extended to include adblocking power-features that Chrome has been removing) including website-specific permissions, optional permissions, and click-to-activate. It does not (as of now) require using Manifest V3, but I think their recent announcement about mobile extensions does require V3, so the writing is on the wall.
The lack of requirements is an issue, but if you're trying to build a sandboxed/secure extension, I'm not aware of any extension security APIs or settings that Chrome has that Firefox doesn't support. Site-specific activation I think works the exact same way. Short-lived background scripts are in there. I'd be curious to hear if there's anything missing. And of course Firefox allows users to disable auto-updating extensions as well.