To a certain extent you can do that with multi-account containers.
For instance, I can have Amazon always open in my “Shopping” tab to keep it separate from my “Social Networks” tab.
Yes to some extent, but no addons, settings, user account, passwords, synchronized stuff etc.
Also afaik you can have profiles be encrypted with different master passwords
I use multiple accounts with Firefox containers, on office.com specifically. One container for my normal account and one for my admin. It works great for me but maybe there are other sites it doesn’t like.