Post a similar screenshot of the files in your sessionstore-backups folder in your profile folder. see screenshots

I wasn’t aware of this. I’ll take a look when back on my PC. (I’m on an ipad at present) Is this something the user has to setup, or does firefox do this up automatically? (hopefully the latter😀)

Here are the screenshots you requested. What am I looking for?

Yes, it's automatic, but it has been reset by restarting or browser updates which is why I make a copy of the folder. see old screenshot I assume your issue happened on the 14th. With Firefox closed, you can make a copy of the file with from the 14th(in your screenshot)and also the one from October. Then change the name of the newly copied file to sessionstore.jsonlz4. Remove the current file with the same name in your profile folder and then move the new file into the profile folder. Open Firefox and see if it restores your session. If the file from the 14th doesn't have the session you're looking for, then you can go back in time going through the same steps with the file from October. The 2nd screenshots is just an old example of the process.

Thanks for that. In this instance it wasn’t a major catastrophe, but it’s nice to know for future reference. I’ll give it a try and see if my ‘forgotten’ websites show up😀

You can often recover your lost tabs by restoring a previous session file: in your Firefox profile folder, look for `sessionstore-backups` and try replacing the current `sessionstore.jsonlz4` with `previous.jsonlz4` or `recovery.jsonlz4` (make a backup first, and do this while Firefox is closed). If those files were overwritten by the second instance, recovery may not be possible. The second instance opened because Firefox sometimes launches a separate “profile” window for promos or onboarding content, especially if triggered by a background update, and Windows treats it as a separate process—unfortunately causing the session overwrite when closed last.

When you realize that you closed a critical window accidentally or out of order, try this immediately, either:

• "3-bar" menu button > History > Recently Closed Windows
• (menu bar or Alt+S) History > Recently Closed Windows

Firefox remembers up to 3 closed windows, so even if you don't realize right away, you usually will be able to recover the closed window.

More generally, the safest way to quit Firefox (from the perspective of preserving your session) is through the menu. Either:

• "3-bar" menu button > Exit
• (menu bar or Alt+F) File > Exit

The second instance opened because Firefox sometimes launches a separate “profile” window for promos or onboarding content, especially if triggered by a background update, and Windows treats it as a separate process—unfortunately causing the session overwrite when closed last.

Since Firefox has a specific meaning for "profile", I wouldn't use that term in this context. Usually the culprit is a popup or pop-under window in the same session.

Yeah this does seem like it opened up another Firefox Window and did not notice and went about closing Firefox with the X on the windows instead of "3-bar" menu button > Exit or (menu bar or Alt+F) File > Exit as this will close all that is open at once.