Is there a browser splitscreen with unique cookies?

Question

Opera

Task: test the service on the topic of customer interaction. For example, buyer-seller. You can log in in one browser as a buyer and in another as a seller, but switching between browsers is tiring (not much, of course). At the same time, there are plugins for Firefox and for Chrome that can split the screen in half or more. This is already better, but I would like each screen to go through its own cookies. How to achieve this?
Thank you for your attention, friends.

Answer 1

Now all browsers have a private mode (InPrivate Browsing)

Answer 2

There is a private tab in both Firefox and Opera.