The Resumable In-Private Browser is a feature that allows you to launch a "Containerized" web browser that stores all cookies, session tokens and other such information.
This is generally used to "containerize" a 2FA authentication process so you can later resume or share it.
Launching the Browser
To launch the Resumable In-Private Browser, open up Universal Migrator and go to Utilities > Resumable InPrivate Browser:
Once you click the button, a dialog will appear asking you to choose the storage location. Should you choose a location like:
C:\__MIGRATIONS\FirmDomainName.com\
Once you choose a folder, a browser will launch. Do whatever work you need to do inside that browser (like signing into 2FA-protected resources) and then close just the browser.
When you do, a folder named __PRIVATE_BROWSER_CACHE will be created in this folder:
If you want to share 2FA access with another member of your team, ZIP this folder and provide it to them.