Does that list stay empty if you open and close some tabs ?

If you close and restart Firefox then this list is saved as part of session data in sessionstore.jsonlz4 in the profile folder.

This data is not saved if you use "Clear history when Firefox closes" to clear the browsing history or if you use Private Browsing mode. External cleanup software can also clear this data.

1/ When I open and close some tabs while the browser is open, that

    history is visible in the 'Recently Closed Tabs' list but when I close 
    and re-open the browser,  the 'Recently Closed Tabs' list is empty!

2/ I do not use Private browsing mode.

3/ Where is the "Clear history when Firefox closes" option in Settings?

    I could not find that.

4/ Do I need to go to sessionstore.jsonlz4 in the profile folder to restore

    the tabs that were closed when the browser was closed?

See:

• Options/Preferences -> Privacy & Security
  Firefox will: "Use custom settings for history":
  [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

The box next to "Clear history when Firefox closes" is *not* crossed on my browser. So, that cannot be the reason I cannot see re-open my tab history when I re-open Firefox.

My current setting is the default option; "Firefox will remember history" .

Thank you for your assistance. I hope you can help to resolve this as it can't be unique for my needs.