I'm not sure about this:

set FF to always restore previous session but closed several multi-tab windows when tabs were restoring

As you noted, Firefox remembers the last 3 closed windows (that's the default value and can be increased, but it's not retroactive). You closed more than 3, so the list here isn't useful? Either:

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

In that case, maybe it would be useful to look at a recent session for reference. It would probably be a day or two old, but maybe? Here's how:

(1) To open your profile folder...

You can open your current Firefox settings (AKA Firefox profile) folder using 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.

(2) Copy out session history files

In your profile folder, double-click into the sessionstore-backups folder. Save all files here to a safe location such as your Documents folder.

(3) What files did you find?

The kinds of files you may find among your sessionstore files are:

• recovery.jsonlz4: the windows and tabs in your currently live Firefox session (or, if Firefox crashed at the last shutdown and is still closed, your last session)
• recovery.baklz4: a backup copy of recovery.jsonlz4
• previous.jsonlz4: the windows and tabs in your last Firefox session => how old is this file?
• upgrade.jsonlz4-build_id: the windows and tabs in the Firefox session that was live at the time of your last update => do you have a recent one from the 145.0.1 update?

Sometimes you can tell from the last modification time which one will have your missing tabs, but not always.

Optional File Contents Preview

These compressed files are a pain to view, so I created a tool to list out their contents. If you want to try that, you can open either of the following pages:

• On my site: https://www.jeffersonscher.com/ffu/scrounger.html
• On Github: https://jscher2000.github.io/Firefox-File-Utilities/scrounger.html

Drag and drop a session history file onto the large box to decompress it. Then click the "Scrounge URLs" button to extract the contents into a readable format.

If you don't get a list within 15 seconds, that probably means the script is caught in a loop. You may need to close the tab to avoid a tab crash and then try again in a new tab.

If you get a useful list, use the "Save List" button to archive it as a web page of clickable links for future reference, in case no other approach is successful.

If you decide you want to roll your Firefox back to one of the older sessions, see the following articles for the steps: How to restore a browsing session from backup.

Sorry, one other thought:

In case some critical windows are not currently visible -- for example, they are positioned off the screen due to a glitch or on a second desktop -- could you open Firefox View and check the Open Tabs list? It should have a box for each open window regardless of whether it is currently visible. If a window is open here, that would explain why it isn't on the Recently Closed Windows list.

Ref. Firefox View - Access pages from open tabs, recently closed tabs, tabs from other devices and browsing history

thank you so much.

i've been relying on the power option "Sleep" too much so possibly have missed some updates. i do remember an update took place, but for now, i'm just working with "Search History" and using urls to reopen some things.

However, when i do that, i also achieve restoring the entire window and all its tabs! seem to have had that do the trick - or enough of it to permit me to continue "from where i was."

thank you for all your advice and links. i will collect pertinent urls to a separate "IJIT" folder ... we'll see. search history is for now where i'll focus, to learn how better to use it.

made the new I J I T folder and moved bookmarks from history. i believe the more i work with "Show All History" the easier it will become finding future "lost by me" pages. [ the update could have happened just as i was looking at 'SAH' - so fast i barely noticed it and possibly Library window ... got updated ... and i felt the pages were "lost by me".

i feel like i got a LOT of help just knowing you're "there", 'Dr.jscher2000'.