Firefox has a short memory: only one previous session, unfortunately. Normally, once you close and reopen and close, that earlier session can no longer be restored.

Sometimes if you're lucky a backup of an earlier session is available. For example, Firefox makes an extra copy just before doing an update, and Windows may create a restore point from time to time.

If you want to try the file from your last update, here's how you would do it:

From inside Firefox, 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. Most likely you'll see one starting with upgrade.js- from the past couple of weeks when Firefox 39 was installed.

Return to the main level of your profile folder.

Leaving that window open, switch back to Firefox and Exit, 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.

Next, copy the upgrade.js-... file you want to try into this folder and rename the file to sessionstore.js

Note: By default Windows hides the .js extension. To work with file renaming more easily, you can set Windows to show ALL file extension using the method in this article: http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions

Start Firefox back up again. When you use History > Restore Previous Session, it should read in that older file.

Does it work?

Thanks jscher, you were my hope funny enough, I was looking your other posts...I have all folders visible in windows, yet, can't locate sessionstore.js. My folder contains previous.js and recovery.js, next to recovery.bak and upgrade.js-20150630154324. Anyway, I renamed the upgrade into sessionstore, and it does work, but restores a more recent session. I don't think there is much to do, I installed the session manager app for the future. If you have another suggestion, please go ahead, will try anyway...

You can try to restore a previous version of the sessionstore.js file.

• Right-click: Properties > Previous Versions
• http://windows.microsoft.com/en-US/windows7/Previous-versions-of-files-frequently-asked-questions