App (pinned) tabs and Tab Groups (Panorama) are stored as part of the session data [1] in the file sessionstore.js [2] in the Firefox profile folder [3].

Make sure that you do not use "Clear Recent History" to clear the "Browsing History" when Firefox is closed because that prevails and prevents Firefox from opening tabs from the previous session.

• https://support.mozilla.com/kb/Clear+Recent+History

• [1] http://kb.mozillazine.org/Session_Restore
• [2] http://kb.mozillazine.org/sessionstore.js
• [3] http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox

It is also possible to use the "Show my windows and tabs from last time" setting, that is usually a more reliable way to restore session data.

• Firefox/Tools > Options > General > Startup: "When Firefox Starts": "Show my windows and tabs from last time"

If you use cleanup software like CCleaner then make sure that Session is unchecked in the settings for the Firefox application.

• App Tab Initializer: https://addons.mozilla.org/firefox/addon/app-tab-initializer/

Thanks for the speedy reply. I already had all the Show My Windows, and Remember History. I also had the Firefox options un-checked in CC Cleaner. I have downloaded the app-tab-initializer, and here's hoping that I will no longer have the same problems ;) , it did happen earlier on this evening again tho, before I installed the app initializer. Thanks again :)

You're welcome