short version: how do I limit session-restore to only restoring my previous session, and not opening older tabs also?

Normally when you exit Firefox, it accurately notes which windows and tabs were open so that when you restore, it reflects that state in the session history file. If you are getting rolled back to a different point, there might have been a problem with the latest file, so Firefox had to fall back to an older one. Or... gremlins.

You could try hiding all of the older files after your next shutdown and see whether that helps work around this problem. Here's how:

Before using the Exit command:

Open your profile folder from the Troubleshooting Information page. Either:

• "3-bar" menu button > Help > More Troubleshooting Information
• (menu bar) Help > More 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 Windows' File Explorer listing the contents of your current profile folder.

Leaving that window open, switch back over to Firefox and use either

• menu > Exit
• (menu bar) File > Exit

After Firefox shuts down:

A new file should have appeared in the profile folder in Windows File Explorer:

sessionstore.jsonlz4

(It's a compressed file, so you can't easily check its contents, but it should have a fresh date/time.)

Assuming that is all good:

Right-click the sessionstore-backups folder, click Rename, and add OLD to the end, to hide it from Firefox:

sessionstore-backupsOLD

Firefox will create a new sessionstore-backups folder when you start it up again, but in case something goes wrong, we can help you mine the OLD folder for windows/tabs as needed.

It may take some time to know whether this cures the problem or whether it will recur randomly.

We have had two threads, I think, in recent years about users whose real-time session history file (recovery.jsonlz4, kept in the sessionstore-backups file while Firefox is running) suddenly stopped updating in mid-session. I can't recall whether this was ever solved.

By the way, if you don't normally use the Exit command, but let Windows tell Firefox to close itself, if Firefox isn't prompt, it may get terminated by the system, i.e., crash. This can lead to unpredictable results.

If you close Firefox directly after closing a lot of tabs then the sessionstore files may not get update. You can try to wait a bit longer before closing Firefox to ensure that the sessionstore files gets updated properly, especially in case when a lot of tabs and windows need to be saved.