You may have corrupt sessionstore [v56] sessionstore.jsonlz4 file(s). Delete all sessionstore* files and the sessionstore-backups folder.

Type about:support<enter> in the address bar.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.

Locate the above file. Then rename or delete it. Restart Firefox.

Don't delete the files if you need to rescue any data from them, just move them out of the profile folder to some location where Firefox doesn't look for them. You can try to read out their contents using this tool: https://www.jeffersonscher.com/res/scrounger.html

Hi ArSparfell, did you already back up all of the contents of the sessionstore-backups folder in your currently active profile? I'll list out the steps at the end as a double-check.

Is there anything else that suggests you went into a time machine and started up in a different (older) profile, such as missing recent bookmarks, recent add-ons, etc.?

Session History File Backup

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 > 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 "Open Folder" (or "Show in Finder") button.

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
• various .js files from Firefox 55 or earlier

Could you take a look at what you have and the date/time of the various files to see whether you think any of them would have the missing tabs?

To preview the contents of a file, you can drag and drop it onto this page, then click Scrounge URLs: https://www.jeffersonscher.com/ffu/scrounger.html

That tool is on my site, so please let me know if it doesn't work for you.

I tried this but it did'nt restore my old session, but the new one.

Did I miss something? What should I do after that "Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox." ??

ArSparfell said

I tried the solution of this thread, but it did'nt work (I don't find any sessionstore.jsonlz4 file in my profile) https://support.mozilla.org/en-US/questions/1234892

If Windows created the snapshot while Firefox is running, you'll want to look for recovery.json in the sessionstore-backups folder instead.

When exporting the file, please save it in a safe location such as your currently live Documents folder (not the Documents folder inside the restore point) rather than directly into your live Firefox profile folder.

jscher2000 said

(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
• various .js files from Firefox 55 or earlier

Could you take a look at what you have and the date/time of the various files to see whether you think any of them would have the missing tabs?

I have two kinds of files when I do this.

- Some form 2017: Two “javascrip” files: Recovery Previous

one Recovery.bak

And three Upgrade.js-[date in 2017]

- others from 2018: Recovery.jsonlz4 Recovery.baklz4 Previous.jsonlz4

three Upgrade.jsonlz4-[date] One of this is from today, but it seems that it contains my tabs from 2017. Another one if from the 1st of November 2018, and contains tabs I had at that moment. I doesn’t seems I have any file with yesterday’s tabs.

(I copied them in my documents, there are not in the “sessionstore-backups” folder anymore.)

Hi ArSparfell, it sounds like Firefox started up in the wrong profile. Do you recall Firefox asking at any point about what profile you want to use??

Let's see whether we can locate something more recent. This is a copy/paste so you can skip steps you've already tried.

Recovering Data After Complete Data Loss

If you haven't already, you may want to do a normal Windows shutdown and startup to release any file locks and complete any pending updates.

If your Firefox data does not magically reappear, the most likely scenarios for complete data loss are:

(1) A Refresh started but the migration of data from your old profile to your new profile was incomplete, or
(2) Your old profile was locked, so Firefox ignored it and created a new one.

It's a lot of things to check, but if you go step by step, it's not too bad.

(1) Did Firefox perform a Refresh?

Unless it was interrupted in progress, you should find a folder on your desktop named Old Firefox Data. Inside would be a semi-randomly-named folder (like a1b2c3d4.default) with freshly updated files. Do you see anything like that?

If so, we'll suggest how to rescue key files or completely restore the earlier profile folder.

If not...

(2) Does the Profile Manager list your immediately previous profile folder?

To check on that, inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

This page should list all the profiles Firefox is currently aware of. If you see a profile that is not currently set as default that looks promising, scroll down to it and click the Set as default profile button below that profile, then scroll back up and click the Restart normally button. (There are some other buttons, but I think those are still "under construction" so please ignore them.)

Firefox should exit and then start up using the other profile. Is that the right one?

If it's not there...

(3) Did Firefox orphan your old profile folder?

Here's how to check whether there are additional profile folders in the standard location in addition to the one you're using. Start by opening your current Firefox profile folder using either:

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

In the first table on the page, click the "Open Folder" button, to launch a new window listing various files and folders in Windows Explorer.

In the Windows Explorer address bar, click the capitalized word Profiles to move up one level in the folder hierarchy. More than one folder here by any chance? Do the files in those folders look like they were last updated around the time of the update?

If you've got any promising looking folders, we can discuss next steps to recover use of them, and any bookmark backup or other useful data files they contain.

Hi jscher2000 ! Thanks for your help !!

I restarted. Windows repaired for a while (as it already did after the crash, and the first normal restart), but nothing changed.

Do you recall Firefox asking at any point about what profile you want to use??

No, Firefox never ask what profile I want to use, at any point…

Unless it was interrupted in progress, you should find a folder on your desktop named Old Firefox Data. Inside would be a semi-randomly-named folder (like a1b2c3d4.default) with freshly updated files. Do you see anything like that?

No, there’s not anything like that.

By the way, after my PC crashed, when I reopened Firefox and Firefox asked me if I wanted my session restored, I noticed that when I open a new tab, all my “most visited sites” had been rearranged, they were on one line instead of two, etc My toolbar got totally rearranged too. And also, my last firefox update was on the 16th of November.

Firefox should exit and then start up using the other profile. Is that the right one?

Firefox only displays the default profile. It doesn’t seem I can choose any other one…

More than one folder here by any chance? Do the files in those folders look like they were last updated around the time of the update?

Hmm, I'm having trouble imagining out how your Firefox got hooked up with such an old profile folder.

Since there doesn't seem to be anything helpful in your current Windows user profile, that is, here:

C:\Users\username\AppData\Roaming\Mozilla\Firefox\Profiles

is it possible you have another Windows user that might have more recent data? If you haven't already, you'll want to turn on viewing of hidden files and folders when exploring:

https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

If there are no other users with your recent data, then the restore points were the one remaining hope. I don't know if November 1 is the most recent available, but if there wasn't a restore point captured after November 16th, it might be.

is it possible you have another Windows user that might have more recent data?

If there are no other users with your recent data, then the restore points were the one remaining hope. I don't know if November 1 is the most recent available, but if there wasn't a restore point captured after November 16th, it might be.

Again, thanks for your help!!

ArSparfell said

How do I know if there is a more recent restore point?

I would only know how to look in whatever ShadowExplorer or System Restore Explorer shows you. I was told about a couple other, similar tools if you think they might be able to see more:

• https://www.nirsoft.net/utils/shadow_copy_view.html
• https://www.nirsoft.net/utils/previous_files_recovery.html

It is possible you still had an old sessionstore.js in the profile folder that Firefox used instead of a compressed sessionstore.jsonlz4 and that Firefox also wasn't able to use a file in the sessionstore-backups folder or Firefox used an upgrade.js file in this folder. Firefox can fallback to .js sessionstore files.

Hi again!

I would only know how to look in whatever ShadowExplorer or System Restore Explorer shows you. I was told about a couple other, similar tools if you think they might be able to see more: https://www.nirsoft.net/utils/shadow_copy_view.html https://www.nirsoft.net/utils/previous_files_recovery.html

It is possible you still had an old sessionstore.js in the profile folder that Firefox used instead of a compressed sessionstore.jsonlz4 and that Firefox also wasn't able to use a file in the sessionstore-backups folder or Firefox used an upgrade.js file in this folder. Firefox can fallback to .js sessionstore files.

Well, if there is no other option, like it seems, I would like to go back to the Upgrade.jsonlz4 from the 1st November which seems to have the tabs I had at the time. How do I do that?

Thanks!

Unfortunately, there's no (easy) way to merge tabs from an old session history file with your current one. Depending on how many you need open immediately, it may be simpler to Scrounge the URLs and save them as a page of clickable links, and then open the desired pages/tabs when needed.

Hi!!

Ok. I did that with the most important tabs, and I let the other ones go...

What can I do to prevent the same thing to happen to me again??

Thanks again for your answers and your help!!

Hi ArSparfell, you could:

(A) Make regular backups of the sessionstore-backups folder. Since this is privacy-sensitive (history+cookies), you may want to be careful where you store it.

(B) Use a session store add-on that saves tabs into Bookmarks, which Firefox backs up daily in the bookmarkbackups folder. For example:

• https://addons.mozilla.org/firefox/addon/session-sync/
• https://addons.mozilla.org/firefox/addon/my-sessions/