Could you check whether you can recover windows from one of these menus:

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

Note: Each window also has its own Recently Closed Tabs list, too.

Unfortunately I can't get anything back.

Okay, here's the next thing to check. Firefox creates numerous session history files that you should back up ASAP.

(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. On that row, 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

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?

Optional Preview

These files are compressed and therefore their contents are difficult to view. I have a tool on my website which can listed out a file's contents. To use it, drag and drop a file onto the large box toward the top part of the following page, then click Scrounge URLs:

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.

I did as you wrote. From the file "upgrade.jsonlz4" it only looks for the google start page. It was the same situation as I wrote earlier. Firefox turned off by itself. After a while a window appeared with the message that firefox has crashed. This window asked if I want to restore the previous session. Of course, I chose the button restore sessions. Then a window appeared with the message that firefox is updating. After a while, firefox only started from the google start page. I tried to restore the previous session using the button in history but it was not possible.

What now ? is there any chance of recovering a lost session?

The upgrade file only has one tab with one URL? And the other files in the folder didn't have anything more?

If you had these tabs open for a while, you could look at "Previous Versions" (available in Windows 7, but not later versions).

Right-click recovery.jsonlz4, click Properties, then click the Previous Versions tab. Windows will check recent restore points for any available copies of the files. You can copy/export the file to a different folder for previewing to see whether it's useful. Also repeat this process with recovery.baklz4 and previous.jsonlz4.

Anything useful there?

Made it :) Even before you wrote, I found the previous file like this. I tried different options and finally succeeded. I'm very happy. Thank you very much for all the answers, for your time and this tool to display the contents of "recovery.jsonlz4" files. I close the topic. Problem solved. Thanks for the help ;)

You can check if you have an "Old Firefox Data" folder on the desktop in case the Refresh feature in Firefox has been used and a new profile has been created.

• https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems

You can also check for previous versions of sessionstore.jsonlz4 in the main profile folder (i.e. not in the sessionstore-backups folder in this folder).

Thanks. Problem solved ;)