Do not close Firefox. First, try to rescue the following files:

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 in Finder" button.

In the window that launches, scroll down:

(1) Double-click into the sessionstore-backups folder. Anything from the relevant date/time? If so, copy it to a safe location such as your Documents folder or Desktop.

(2) Back at the main level, scroll down to the sessionstore file(s). Same question. If so, copy it to a safe location such as your Documents folder or Desktop.

The kinds of files you may find among your sessionstore files are:

• sessionstore.js and recovery.js: the windows and tabs in your currently live Firefox session (or, if Firefox is closed, your last session)
• recovery.bak: a backup copy of recovery.js
• previous.js: the windows and tabs in your last Firefox session; sessionstore.bak for pre-33 versions of Firefox
• upgrade.js-build_id: the windows and tabs in the Firefox session that was live at the time of your last update; sessionstore.bak-datetime for pre-33 versions of Firefox

If you come up with something promising, you may be able to have Firefox use it for your next session (details if relevant).

Thank you for your prompt reply. Unfortunately, I'd already closed Firefox trying to figure this out on my own before contacting you. However I've tried to follow your other suggested steps. Here's screen shots of the files I've found. Not sure what next steps are. Also...is there a way we can do a screen share session?

I run Windows, so I'm somewhat helpless on Mac and Finder. I suggest copying all those files to a safe location first.

You may need to switch the view of the file list to one that shows dates and times to get a better sense of which file might have the most recent relevant data.

Thank you. I'd already copied all relevant files to a new folder per earlier suggestion above. Here's an image showing the list view of the contents in the sessionstore-backups folder. Also, when I click on the other two files (sessionstore.bak and sessionstore.bak-2...) I get the following message (see other attached screenshot). Is perhaps what I'm needing to work with in those 2 files I can't open?

What I'd REALLY need to do is to somehow restore back to a specific session...for example yesterday anytime. I'm still not clear how to do that. Is there anyone else there familiar with the Mac, and/or can we do screen share session so I can be walked through this process?

Firefox's session history is only one session deep, so if you aren't able to Restore Previous Session immediately after starting Firefox, then there's no way to go back in time. On Windows, an OS update usually generates a "restore point" and that creates the possibility of extracting the earlier file from that system feature. I don't know whether Mac has anything like that.

When I look at the file sizes in your sessionstore-backup folder, I can see that as of the Nov. 10 update, your session history file was 100x larger than it is now. If sessionstore.bak is not large enough to plausibly have your previous windows and tabs, then you probably need to go back to that Nov. 10th file and hopefully that will get you the most critical ones.

Because session restoration changed recently, I'm not confident giving you specific steps to do that off the top of my head. Let me look into it a bit further.

Regarding .bak files, they contain a data structure that Firefox would read to recover your windows and tabs and there is no way to launch them directly.

Thank you...I really appreciate you looking into my options a bit further. That's too bad Session History only goes one session deep. If would at least go 2 or 3, it would certainly solve a lot of peoples headaches regarding this common problem. Feature request?

Also, if I decide to try restoring my November 10th session, can you walk me thru the steps I'd take to at least do that?

Thanks again.

Okay, let's give this a try. You'll need to translate to Mac if I describe something that doesn't make sense.

First, you already have your profile folder open. When you quit Firefox, a file named sessionstore.js should appear with a fresh date/time. This contains your windows and tabs from the session you just closed out. Rename this file to sessionstore.old (or other name of your liking). (For example, on Windows, you could right-click>Rename the file. If Windows is hiding the .js extension, you need to put the new name in quotation marks "sessionstore.old" to make sure it overrides the .js extension.)

Next, copy the upgrade.js-1020112145 file into the folder, and rename it to sessionstore.js. (For example, on Windows, you could right-click>Copy the file from the sessionstore-backups subfolder or the safe location and right-click>Paste it into the profile folder. Then right-click>Rename the file.)

And now start Firefox up, and use Restore Previous Session to load the windows/tabs as of Nov. 10th.

Does that work?

There is an extension named Session Manager that allows you to save older session files, and even to save them outside of Firefox's profile folder. I don't use it myself, but it has come up here many times (usually in a positive light). More info: https://addons.mozilla.org/firefox/addon/session-manager/

I'm not sure Firefox will ever add that as a native feature. It's already so confusing explaining how the various privacy options interrelate...

Do you have older versions in the Time Machine if you use this on your Mac? If that is the case then try to restore the sessionstore.js file(s) from that backup.

• http://www.apple.com/support/timemachine/

I tried the last suggestion you shared multiple ways/times, and unfortunately that didn't work. Also I did not have the Time Machine app installed, so that's not an option either.

Next steps or suggestions?

What happened - did Firefox mention an error opening the renamed file, or was Restore Previous Session grayed out? This is all I've got, so we need to make it work. ;-)