How to open or view two accounts at the same time.

I hate that the drop down thing for the second account is gone. That was a convenience yall took away from us. And Outlook is suppose to better! How????
So since that is now gone and heaven knows why I thought maybe I could keep both my accounts open during the day for my convenience but,  can't figure a way of doing that. Very time consuming to have to continually open one sign off and go to the second one. What is wrong with you people?
Sue