If you're using #firefox, I can highly recommend the Multi-Account Containers extension: https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/
It separates cookies and sessions so you can log into different accounts on the same site. Or use it to quarantine Google/Facebook stuff!
@edwardloveall you don't get to use it if you're using private browsing by default. It works well otherwise.