You have to close individual tabs by using "x" to close them and if you reopen them Firefox session should restore only those last opened back. Is that not working or something? But if you open Firefox and don't choose to restore last session those will not be available the next time you start Firefox. They will be in the "history" listing only then.

There is a Addon if you search the Firefox Addon page but if it works depends on what your asking it to do.

https://addons.mozilla.org/en-US/firefox/addon/tab-session-manager/

You have to close individual tabs by using "x" to close them and if you reopen them Firefox session should restore only those last opened back. Is that not working or something? But if you open Firefox and don't choose to restore last session those will not be available the next time you start Firefox. They will be in the "history" listing only then. There is a Addon if you search the Firefox Addon page but if it works depends on what your asking it to do. https://addons.mozilla.org/en-US/firefox/addon/tab-session-manager/

I would like to keep enabled the setting that preserved windows when quitting and reopening FF. I am already using Tab Session Manager to archive larger sessions, but I don't always want to archive a session before quitting. I am looking for a manual way to close all open windows (thus all open tabs) without manually closing each window (since I have many windows open).

Then you need to go to Firefox Addon page and search for something that your asking for.

See feature request.