Administrating multiple Office 365 environments - Best Practice

Differnet browsers, private sessions, even running them on different machines as switching tenants seems to leave some artifacts (often experienced with the Partner admin portal).

For PowerShell, I've cooked a small script that brings up a UI dialog allowing me to choose a predefined credentials, or enter new ones if needed. Again it's best to use separate environments, I've personally wiped all users in the wrong tenant once or twice by mistake :)