Enter about:config in the URL bar and set browser.sessionstore.max_windows_undo = 6.

I did, changed the value from 3 to 6, and also tried 10.

Nothing new. It even now does open recent 2 only.

Usually it's working. Have you restarted the browser?

So is there any way I can happen to restore (previous sessions) for more than just 3, or at least that were open on a certain day ??

If you have ever checked the contents of the sessionstore-backups subfolder in your Firefox profile folder, you'll notice that Firefox creates numerous session history files. However, because session history is only for the currently and immediately previous sessions, it is rarely possible to recover earlier sessions. But there are a few things you could look at:

(1) Update snapshots. When Firefox installed the 80.0 and 80.0.1 updates, it should have made snapshots of your session before shutdown. Perhaps that was too long ago, but if you tend to keep tabs open for a long time, it could help. More on extracting that list in a bit.

(2) Erased files. I don't know how often Firefox deletes the recovery.jsonlz4 file (during your session? only at shutdown?), but a program like Recuva can sometimes "unerase" a recently deleted file. https://www.ccleaner.com/recuva

(3) Shadow copies. Windows occasionally makes copies of Firefox profile folder files, but these might be your oldest option. More details below.

The sessionstore-backups folder

(1) To open your profile folder...

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, find the Profile folder row and click the "Open Folder" button. This should launch a new File Explorer window.

(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

To preview the contents of a file, you can drag and drop it onto a tool on my site:

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

Click the Scrounge URLs button to extract a list of clickable links from the file. If the list looks useful, click the Save List button to keep it on your system.

Shadow Copies

You can use a utility program to search inside restore points to try to locate an old file that's usable. (Please do NOT try to use the built-in Windows System Restore for this because you probably would lose data.)

First, set Windows to show hidden files and folders: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

Then download and run one of these two programs:

• ShadowExplorer: http://www.shadowexplorer.com/
• Shadow Copy View: https://www.nirsoft.net/utils/shadow_copy_view.html

Within the most recent restore point shown in the program, you can explore along this path to see whether you can find a shadow copy of your profile:

\Users\your-user-name\AppData\Roaming\Mozilla\Firefox\Profiles\your-profile\sessionstore-backups

You can export any promising recovery.jsonlz4 / previous.jsonlz4 files to a convenient location such as your currently live desktop.

Then to see what is in them, you can use the Scrounger tool mentioned in the previous section.

Note that Private Browsing mode are never included as part of Session Restore.

Quote: I am trying not to open new more windows and are using Private browser so I don't need to open more Firefox 'new' (windows)

If you use Session Restore to open tabs from the previous session automatically then it shouldn't make a difference how many tabs or windows you reopen and all open windows should be restored if you use Exit/Quit to close the Firefox application and not the close X. The above mentioned undo pref only applies when you want to restore a closed window during a session or from a restored session (History -> Restore Previous Session).

This sounds more that sessionstore.jsonlz4 isn't created properly and doesn't have all session data.

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

I had a post I wrote previously, but it went as I 'chose the solution' :(

Anyway.. It mainly included, I am deeply thankful for all the efforts even if this did not end up working. This is probably the best support I have ever experienced. Not only is it very helpful and precise, but also quick that I am the one late to reply :D

The sessionstore-backup folder is what worked for me, probably a little thanks for me being lazy and keeping them open, yet it is mainly thanks to you mentioning that @jscher2000 so thank you the most !

Endless thanks for all of these. And I still wonder why the solution of @TyDraniu did not work. Though I did restart the browser, and restarted the pc just in case too.

As for @cor-el thanks for your contribution. I am aware of this, I just meant that I am running a Private browsing in parallel just for the (CRTL + SHIFT + N) purpose.

Thank you all very very much :)) This is why I love Firefox.

All the best, and stay all safe.

And just for information, this was with version 80.0.1