Yeah, and also I’d like it to ask me what container to open for a website sometimes, out of remembered ones. E.g. I have a website I use in just two containers (out of 15), and I like it to ask each time I open a new instance, so I won’t have to choose out of all my instances, just those two.

Fantastic idea, besides the UI needed it should be manageable to implement.

The UI is already partially there. You can choose which extensions are enabled in private Windows. It's a matter of extending that to containers.

Why not use about:profiles?

Because I can't run different profiles in the same window. Also, the profiles don't share bookmarks.

What's your use case for that? Just wondering.

For example, testing website functionality without an ad blocker.

Honey / Rakuten are very useful extensions, but I don't want them having access to every site I visit.

In Chrome I use profiles and set up those extensions on my "shopping" profile only.

In Firefox I use containers, but can't isolate these extensions the same way

You can do it with OS-level user accounts.

You can't with containers, they're running on top of a current profile.