Hi TREKE, tab groups are stored in your session history file. When Firefox shuts down normally, this file is named sessionstore.js and can be found at the main level of your Firefox profile folder. While Firefox is running, or if Firefox crashed, your session history is stored in a subfolder named sessionstore-backups under the name recovery.js. When Firefox starts up, it checks for sessionstore.js and, if that isn't found, for recovery.js. Depending on your settings, the file either is restored automatically or is made available through the History menu under Restore Previous Session. For best results, do not try to delete/replace these files while Firefox is running. A few other notes: (1) How to find your profile folders on the respective systems: [[Profiles - Where Firefox stores your bookmarks, passwords and other user data]] (2) By default, Windows hides the .js extension. To ensure that you are looking at the files I mentioned, you may want to turn off that feature. This article has the steps: http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions (3) Some other files you may find in sessionstore-backups are: * recovery.bak: a backup copy of recovery.js * previous.js: the windows and tabs in your last Firefox session * upgrade.js-''build_id'': the windows and tabs in the Firefox session that was live at the time of your last update Does that help? Also: [[Recovering important data from an old profile]]

Note that Tab groups will be removed in Firefox 45 and later versions. *https://support.mozilla.org/kb/tab-groups-removal *Tab Groups: https://addons.mozilla.org/firefox/addon/tab-groups-panorama/