Spoof Server Login Page

The essential problem here is I need to find a way to spoof or otherwise prevent our private office 365 server from auto logging in our users. Sometimes we need to log into different accounts and we can't because the browser sees our credential/user (not sure which) and auto logs in user. There is no defeat in the interface I can use.

Does anyone know a go way to prevent my Browser from passing my company userId or other credential?

I'm currently trying a script to intercept URL strings, but I'm thinking someone must have come up with a solution to this before.