https://support.mozilla.org/en-US/questions/1010551#answer-603360 Also you can try the add on called Session Manager.

Sorry for the delay in responding. Could you check for a pre-update session history file here: Open your current Firefox settings (AKA Firefox profile) folder using either * "3-bar" menu button > "?" button > Troubleshooting Information * (menu bar) Help > Troubleshooting Information * type or paste about:support in the address bar and press Enter In the first table on the page, click the "Show Folder" button. In the window that launches, scroll down and double-click into the '''sessionstore-backups''' folder. Save all files here to a safe location, such as your Documents folder. '''Note: if you do not see a current (updated within the past few minutes) recovery.js file here, then your Firefox may not be saving session history correctly.''' ''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]'' The one I'm particularly interested in finding would be the most recent one that follows this naming pattern: upgrade.js-''build_id'' -- '''for example''' -- upgrade.js-20150525141253 This file should contain the windows and tabs in the Firefox session that was live at the time of your last update. Do you find anything recent like that? This file is not human readable, but can be "switched" for your current session history file to restore the session from that time. If that sounds like it's worth a try: (1) Move up to the main level of the profile folder (the one that opened from Firefox, before you clicked into sessionstore-backups). (2) Leaving that window open, switch back to Firefox and: (A) If applicable, bookmark the tabs you'll want to come back to (Ctrl+d for individual tabs, or to save all the tabs in the window, right-click a tab > Bookmark All Tabs) (B) Then Exit out of Firefox completely using either: * "3-bar" menu button > "power" button * (menu bar) File > Exit Pause while Firefox finishes its cleanup, then rename '''sessionstore.js''' to something like sessionstore.old (in case this all fails and you need it back). (3) Copy the upgrade.js-20150525141253 (or most recent similarly named file) into the profile folder and rename it to sessionstore.js (4) Start Firefox back up again. You may need to use History > Restore Previous Session if Firefox doesn't restore those windows and tabs automatically. Success?

Thanks to both of you for the understanding on how this all works.