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.
island - a free and opensource alternative to parellel space
Multilogin - Connect to websites as a multitude of different users
App Cloner - Clone your Android apps so you can use multiple logins.
Session Box - Using websites with multiple accounts at the same time is made easy.
Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.