Hi, It looks like it is not a Firefox built-in functionality, but could have been added by an add-on. From the wordings it looks like it provides the functionality for saving open tabs for later (offline) reading. You can check the installed add-ons by going to '''Tools''' ('''Alt''' + '''T''') > '''Add-ons''', click '''Extensions''' on the left. If an extension's functionality is not fully visible, click '''More''' and to visit the web site of the extension, click the '''Homepage'''. ............................................................................................................................... Useful links: [https://support.mozilla.com/en-US/kb/Options%20window All about Tools > Options] [http://kb.mozillazine.org/About:config Going beyond Tools > Options - about:config] [http://kb.mozillazine.org/About:config_entries about:config Entries] [https://support.mozilla.com/en-US/kb/Page%20Info%20window Page Info] Tools (Alt + T) > Page Info, Right-click > View Page Info [https://support.mozilla.com/en-US/kb/Keyboard%20shortcuts Keyboard Shortcuts] [https://support.mozilla.com/en-US/kb/Viewing%20video%20in%20Firefox%20without%20a%20plugin Viewing Video without Plugins] [http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox Profile Folder & Files] [https://developer.mozilla.org/en/Command_Line_Options#Browser Firefox Commands] [https://support.mozilla.com/en-US/kb/Basic%20Troubleshooting Basic Troubleshooting] [https://support.mozilla.com/en-US/kb/common-questions-after-upgrading-firefox-36 After Upgrading] [https://support.mozilla.com/en-US/kb/Safe%20Mode Safe Mode] [http://kb.mozillazine.org/Problematic_extensions Problematic Extensions] [https://support.mozilla.com/en-US/kb/Troubleshooting%20extensions%20and%20themes Troubleshooting Extensions and Themes] [https://support.mozilla.com/en-US/kb/Troubleshooting%20plugins Troubleshooting Plugins] [http://kb.mozillazine.org/Testing_plugins Testing Plugins]