Let's say I have an extension that I use for work, that has a work-specific login or API key. I want to keep that plugin separate from the rest of my stuff because it's for work. You can't do that with tab containers.
The profile interface for FF is archaic and hard to manage.
Separate profiles was always a better solution than contained tabs.
And what are those? I have yet to encounter anyone using a extension that contains some sort of work secrets/api. I'm not doubting it exists, but I think it's a use case which is maybe in the 0.00001% (if even that).
On the other hand containers allow me to specify which ones to open on automatically and so I can use lots of different containers for different uses that I want to separate, e.g. Facebook, Gmail, HN... Something lots of people want to do, but you can't really do with profiles (well you could but it would be super annoying). Moreover I can use temporary containers so I have isolated tabs for all the general browsing (all websites where I haven't specified a specific container) with all the tracking information being deleted as soon as I close the tab.
> but I think it's a use case which is maybe in the 0.00001% (if even that).
Actually password managers are very common, and immediately relevant to this conversation. I have a password manager for work, and one for personal. That puts us a bit higher than your pretty dismissive 0.00001% estimate.
Literally the first thing that came to mind and there are many more examples.
I use a tool called Junction which allows me to choose which browser opens up a link, which solves for your second issue.
Isolated browsers are much better than isolated tabs.
The profile interface for FF is archaic and hard to manage.
Separate profiles was always a better solution than contained tabs.