Normally, if your Firefox is set to restore your previous session tabs and windows, it just works. Did you Exit Firefox before restarting your system? That usually gives you the best chance at a clean startup, compared with letting Windows close Firefox, which can lead to closed windows. To find closed windows:

(1) First check whether session restore did not run. In that case, these are usually available:

• "3-bar" menu button > History > Restore Previous Session
• (menu bar) History > Restore Previous Session

(2) If your session was restored in part (or Firefox thinks it was), then check for any of these:

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

What if there's nothing there? If your Taskbar button gives the impression that Firefox windows are open but they aren't visible, then you may need to clean up or delete the settings file related to window positions.

If that isn't a factor, it's possible that your session history files were not used or got corrupted. You may want to check the following:

(A) Old Firefox Data

If a Refresh ran (sometimes called a Tune-up), there will be a new folder on your Windows desktop named Old Firefox Data. If you see that folder, check inside to see how fresh the files are before proceeding.

(B) Current Profile Backups

Firefox creates snapshots of your session history during automatic updates, and even if it has been a while, there might also be other files. Here's how to investigate those:

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.

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

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.

(C) Other Profile Backups

In case Firefox started up a new profile -- usually it doesn't have any of your data until you sign in to your Mozilla Account and get Sync going -- you could investigate other available profiles. Let us know if that sounds like a road you want to go down.

Yes, I exited Firefox before restarting. Restore Previous Session is not available under History. The Profile folder had current files with yesterday's dates, times close to when I lost the tabs, nothing that contained my lost tabs. There was no Old Firefox Data folder on the desktop. In Library I found Import and Backup. The drop down menu showed the option Restore. I chose June 6 as the date to use as a Restore point and got most of the tabs back. Thanks for answering.

What files do you see in the sessionstore-backups folder?

You will normally find these files in the sessionstore-backups folder:

• previous.jsonlz4 (cleanBackup: copy of sessionstore.jsonlz4 from previous session that was loaded successfully)
• recovery.jsonlz4 (latest version of sessionstore.jsonlz4 written during runtime)
• recovery.baklz4 (previous version of sessionstore.jsonlz4 written during runtime)
• upgrade.jsonlz4-<build_id> (backup created during an upgrade of Firefox)

You can copy a file with Firefox closed from the sessionstore-backups folder to the main profile folder and rename the file to sessionstore.jsonlz4 to replace the current file.

• make sure to backup the current sessionstore.jsonlz4

You can look at this tool to inspect a compressed jsonlz4 sessionstore file. This tool works locally, no uploading done.

• https://www.jeffersonscher.com/res/scrounger.html

I am on my other computer where I did not have the problem. Similar posts came up like the one you just posted. It is too long after the fact for us to look at what might have been there in terms of file names. Nothing was there that would have restored my tabs. Anyway, I restored some by manual search under History and by the process I already described. Under Extensions I added Tab Session Manager.