OneTab - Whenever you find yourself with too many tabs, click the OneTab icon to convert all of your tabs into a list. When you need to access the tabs again, you can either restore them individually or all at once.

Firefox Multi-account Containers - Sign in to two different accounts on the same site

Workona - A better way to work in the browser.

Lightbeam for Firefox - Mozilla is the not-for-profit behind the lightning fast Firefox browser. We put people over profit to give everyone more power online.

Session Buddy - Manage Your Browser Sessions

Multilogin - Connect to websites as a multitude of different users