There are two prefs on the about:config page that control how many tabs (25) and windows (3) can be restored. You can increase max_windows_undo from its default value of 3 to a higher value to be able to restore more closed windows.

• browser.sessionstore.max_tabs_undo = 25
• browser.sessionstore.max_windows_undo = 3

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Thank you for the answer, but I don't think that's what I meant because I don't need more than 3 windows, but as a result of an emergency shutdown of the computer, 3 windows with a dozen or so tabs each were closed, including the ones I care about and I can't restore them because the window restore function is grayed out. and I can't restore even one window from 3

You may first have to restore the previous session to be able to reopen windows.

Backup the session files in the sessionstore-backups folder in the Firefox profile folder to make sure not to lose possible important session data. Do NOT close Firefox when Firefox is already running.

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

• 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

Thank you very much, you saved my windows and tabs a hint for others who will be looking for these files 1. the current sessionstore.jsonlz4 file is created only when the browser is closed 2. in the sessionstore-backups directory, look for files with dates, for me only the fourth one (almost the oldest one) worked, but since the failure I closed the windows many times

It turned out that the browser update closed the windows and disabled the ability to open recently opened windows from the menu by default. Thank you again for your help cor-el

Unfortunately, the situation repeats itself every few days. I close 3 windows when I shut down the computer and only one opens the next time I turn it on and I cannot open the last closed windows. the method indicated above helps to restore it, but it is very cumbersome and the last few tabs are always missing.... is there a way to save the last open tab and all windows in recovery.jsonlz4

You can use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar, especially if you have multiple windows or Private Browsing windows open to prevent losing tabs in unnoticed windows.

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

You can also select to reopen the tabs automatically for more safety.

• Settings -> General -> Startup: "When Firefox starts": "Open previous windows and tabs"
• https://support.mozilla.org/en-US/kb/restore-previous-session

firefox doesn't save any backup or deletes the last file for some reason? On October 22, 2023, I worked on 3 windows then on October 23, 2023, after opening the browser, there was only 1 window and no tab and the previous and recovery files only from today after opening this single window (I attach a screenshot) I have already started manually copying the closed session file from time to time, but it is not possible every day Is there an option to save at least the last 2 days? I did the window settings as you wrote to me earlier:

    browser.sessionstore.max_tabs_undo = 25
    browser.sessionstore.max_windows_undo = 3