Luckily you are still on Windows 7. The only copy of Windows besides Vista that has a auto backup feature of your files called "Previous Versions". Win 8 and higher removed this feature sadly and idiotically.

Try this: You have to check for previous versions on the actual Firefox profile folder. It never works for me if you check for previous versions on the individual Firefox files.

So to view the folders, navigate to where your Firefox profile folder lives: C:\Users\[Username]\AppData\Roaming\Mozilla\Firefox\Profiles\[random].default\

Right-click on the [random].default folder and choose Restore previous versions. Choose a folder dated from before this accident and click the "Open" button. You should find a safely backed up sessionstore-backups folder there. ;) Lastly, copy the folder to another safe location and copy it back into the Firefox profile.

Sometimes you will also find a sessionstore.js file in the "Previous versions" of a Firefox default profile folder. You can copy this file as well if you find it and see if it brings back your tabs if the sessionstore-backups folder fails to.

Another person who had success using this method: https://support.mozilla.org/en-US/questions/991618#answer-548192

Unfortunately, when I right-click there are no other previous versions available... I did find a sessionstore.bak file (in another folder) from several days ago. Could this help at all?

Did you refresh (reset) Firefox during your update and created a new profile?

This could happen if Firefox reported that it was starting slowly.

When you refresh/reset Firefox then a new profile is created and some personal data (bookmarks, history, cookies, passwords, form data) is automatically imported. The current profile folder will be moved to an "Old Firefox Data" folder on the desktop. Installed extensions and other customizations (toolbars, prefs) that you have made are lost and need to be redone.

It is possible to recover data from the "Old Firefox Data" folder on the desktop, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

You can also check for multiple profiles in the default location.

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\

Yes, try copying over that sessionstore.bak file to your [random].default folder. Make sure Firefox is closed before doing this. Then rename the file to sessionstore.js. Also rename the sessionstore-backups folder to "old-sessionstore".

Sometimes Firefox will not read the sessionstore.js file if it can detect the other session restore files (recovery.js, recovery.bak & previous.js) in the sessionstore-backups folder.