Hi Bram, that preference doesn't cause Firefox to save more sessions.

Do you have Firefox set to restore automatically at startup (first checkbox on the Settings page)? In that case, check the History menu to see whether you can restore any closed windows:

• "3-bar" menu button > History > Recently Closed Windows
• "Library" toolbar button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows

If that doesn't help...

Firefox creates numerous session history files, but because session history is only for the immediately previous session, it is unfortunately too easy to lose it. Could you start by making a backup of your existing session history files? Here's how:

Do not exit Firefox, or if you closed it, don't re-open it.

(1) To open your profile folder...

If Firefox is still running:

You can open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > Help > More Troubleshooting Information
• (menu bar) Help > More Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, find the Profile Folder row and click the "Open Folder" button. This should launch Windows' File Explorer listing the contents of your current profile folder.

If Firefox is closed:

Type or paste the following into the Windows Run dialog or the system search box and press Enter to launch Windows Explorer:

%APPDATA%\Mozilla\Firefox\Profiles

In that folder, do you see a semi-randomly-named folder? If so, click into it. If you find multiple such folders, find the one that was most recently updated.

(2) Copy out session history files

In your profile folder, double-click into the sessionstore-backups folder. Save all files here to a safe location such as your Documents folder.

(3) What files did you find?

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

• recovery.jsonlz4: the windows and tabs in your currently live Firefox session (or, if Firefox crashed at the last shutdown and is still closed, your last session)
• recovery.baklz4: a backup copy of recovery.jsonlz4
• previous.jsonlz4: the windows and tabs in your last Firefox session
• upgrade.jsonlz4-build_id: the windows and tabs in the Firefox session that was live at the time of your last update

Sometimes you can tell from the last modification time which one will have your missing tabs, but not always.

Optional File Contents Preview

These compressed files are a pain to view, so I created a tool on my website to list out their contents. If you want to try that, you can drag and drop it onto the large box on the following page, then click the "Scrounge URLs" button:

https://www.jeffersonscher.com/ffu/scrounger.html

If you don't get a list within 15 seconds, that probably means the script is caught in a loop. You may need to close the tab to avoid a tab crash and then try again in a new tab.

If you get a useful list, use the "Save List" button to archive it as a web page of clickable links for future reference, in case no other approach is successful.

Tricking Firefox into Using an Older File

If you figure out which older file you want to try, we can provide next steps.

Thank you very much for responding so quickly, @jscher2000. (Aside: That ...max_resumed_crashes idea actually came from a post of yours in that thread. If it's not as I wrote, then can you please clarify what changing that number really will do?)

Yes, my Firefox IS currently set to "Open previous windows at startup". That's been true for a while.

Also, yes, "Recently Closed Windows" IS listed under History in my Menu Bar (but unfortunately that earlier session's windows aren't there right now).

I found the Profile Folder and copied those four (4) files to a new subfolder elsewhere. Unfortunately, the "previous.jsonlz4" file has only 5K (as opposed to a copy of one from 1-1/2 months ago that I also happened to have, and that had 5,304K) so this MIGHT NOT have exactly what I'm looking for -- my hope would be to somehow be able to find a bigger (but still recent) one, of size perhaps similar to the 5,304K version, that preceded the 5K file, please.

On a lark, in File Explorer, I right-clicked on previous.jsonlz4 and looked to see if I could "Restore previous versions", but none were shown as being available.

Thank you for helping me reach this point, but can you please guide me further?

Thanks again, Bram Weiser

max_resumed_crashes relates to the number of times Firefox will try to restore the current session history file automatically before giving up and showing you an error screen.

How recent is the latest file whose name starts with

upgrade.jsonlz4-2023[more digits]

If you installed Firefox 111 in the past 48 hours it may be very timely. Or it could date back several weeks to the last automatic update.

Are there any files that were close in time but just before the crash?

Hi, again, jscher2000, and thanks for following up.

Thanks for clarifying max_resumed_crashes. From how I read your comment in that other thread, I thought it was something else...my mistake.

The most-recent upgrade... file is from 3/1/23. I am now running v110.0.1 (though I think I'd downloaded, but not yet installed, v111, earlier today -- I get a "Restart to Update Firefox" button when I go to Help --> About Firefox).

Unfortunately, the only file in the sessionstore-backups folder that had a date/timestamp near the crash was the 5K previous... file which was made amidst that 45-minute period without a true Internet connection. The next-most-recent one in the folder is the afore-mentioned 3/1/23 upgrade... file.

Thanks again, Bram Weiser

I don't know whether it is useful to roll back your current session to March 1st or whether you just want to create a clickable list of URLs from those tabs for reference.

You can create a list using the Scrounger tool I mentioned before.

If you want to swap the old file for the latest one to roll back your open tabs to March 1st, you can find the steps in the following thread:

https://support.mozilla.org/questions/1396868

That won't affect your browsing history; other pages you visited recently should still be listed in your browsing history (but unfortunately, there is no record there of which ones you still had open).

If you want to export a more minute-to-minute list of history, one that shows all visits to a URL and not just the latest, I can suggest this program that I use:

http://www.nirsoft.net/utils/mozilla_history_view.html

It can read history by a date range and you can save the list to a number of formats.

Hi, again, jscher2000, and thanks for following up.

Ideally, I hoped(!) there was a way to relaunch the tabs (not so much to get a list of URLs for those tabs) from more than one (1) session ago, even if not necessarily all the way back to 3/1/23 (but, if relaunching the 3/1/23 tabs is the best I can do, then that's the best I can do :-) ).

Thanks again, Bram Weiser

Hi, again, jscher2000.

I've followed the steps in that https://support.mozilla.org/questions/1396868 thread and things are mostly back to normal. (I still need to use my History to find what other tabs might have been opened since that upgrade... file was created on 3/1/23, and that were still open when the "crash" happened.)

As such, I marked your post, above, that cited that thread as having "solved the problem" (though the above proviso would nonetheless still apply).

Thank you for taking time to assist me with this!

One more question, please, just so I'm clear on something...can I delete the newly-renamed ...OLD files once I'm persuaded that this restoration was indeed successful (such as, when I next close and reopen Firefox, say, and/or power down my PC and then power up again)?

Thanks again, Bram Weiser

One more question, please, just so I'm clear on something...can I delete the newly-renamed ...OLD files once I'm persuaded that this restoration was indeed successful (such as, when I next close and reopen Firefox, say, and/or power down my PC and then power up again)?

Yes, those were only to be used in case you decided that rolling back was a mistake.

Thank you again, jscher2000. I appreciate your help very much.

Sincerely, Bram Weiser