When accessing multiple Google accounts from the browser, with multiple accounts logged in, Google will allow selecting the proper account using a number that identifies the chronologically logged in user, with the syntax:
https://<service-name>/u/<user-number>/
For instance:
https://mail.google.com/mail/u/0/#inbox
https://contacts.google.com/u/2/preview/all
I wonder if is there a way to use an URL where the user-number is replaced with the user email....