hi anomamy, please enter about:support into the firefox address bar and click on the button to open your profile folder. in there you'll see a another folder labelled sessionstore-backups - first make a backup of that whole folder to a secure location.

then, while firefox is closed, rename the previous.js file (which you should find in the sessionstore-backups-subfolder), into sessionstore.js and copy that file directly in the profile folder (one folder hierarchy up), replacing the existing file with the same name. afterwards when you launch firefox, hopefully the earlier session will be restored...

https://dutherenverseauborddelatable.wordpress.com/2014/06/26/firefox-the-browser-that-has-your-backup/

Thanks, but it didn't work. Firefox reopened w/only 1 page, the start page. That was the immediately previous session, & I want to go back to the session before that. Is there any way to do that? There's a file in sessionstore-backups called upgrade.js-20161208153507 w/a "date modified" that looks like the day i lost the session I want to restore--should I put that in the profiles folder? What about recovery.bak or recovery.js? Doesn't seem likely--they're both dated today. But I might as well ask.

You can copy an upgrade.js-xxxxxxxxxxxxxx file just like one of the other files in sessionstore-backups to the main profile folder and rename the file to sessionstore.js. It is probably best to set the startup setting to "Show my windows and tabs from last time" before doing this. Note that Firefox needs to be closed when you make modifications to files in the Firefox profile folder.

On copying an upgrade: The question is, would it help me recover the tabs & history from my earlier (but not the immediately previous) session if I did that? Would putting a renamed upgrade.js-_____________ file in sessionstore-backups just reset it to the state of the browser as of the date of the upgrade, rather than to where it was before this happened? Would it even do that?

On the startup setting, I had a lot of trouble finding that. I didn't know where to look for it: under History, Tools/Options, or Help. Please include the full path when you say something like "set x setting to y"--it's not obvious to people who don't deal w/it all the time. I did eventually find it in Options, but I'm pretty sure selecting "Show my windows and tabs from last time" would again make it open w/just the tabs & windows from the immediately previous session, not the one I'm trying to get back. So is there any way to get back to that one when there have been 1 or more sessions in between? Could I reconstruct it from what's in "Show All History"?

Finally, yes, I knew Firefox had to be closed when I made those changes--that's what phillipp told me, & that's what I did.

Unless you have a backup copy of that older sessionstore.js file then your only option is to use an upgrade backup.

You can check in Windows Explorer if there is a previous version of the sessionstore.js file available.

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