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.

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

island - a free and opensource alternative to parellel space

Tab Session Manager - Save and restore the state of windows and tabs.

AllAccounts - AllAccounts is an extension that allows Firefox to connect to websites using different user names.