Dinner plan died, so more time to try to find how to shut down safely. Hoping for answers to last 3 posts.

For about:config, the separator is a colon, not a period. That should get around it being converted to a web address.

On the History menu, is "Restore Previous Session" grayed out or enabled?

If it's enabled, and you have no currently open tabs you don't mind losing, give it a try to see whether that auto-restores last night's previous.js.

If it's grayed out, you'll need to do the switch the hard way... The usual method is as follows:

(1) Exit Firefox normally, and these changes should occur:

• recovery.js is moved from the sessionstore-backups folder to the main level of the profile folder and renamed to sessionstore.js
• recovery.bak is deleted from sessionstore-backups

(2) Once Firefox has stopped updating things, rename sessionstore.js to sessionstore.old

(3) Copy in the file you want to restore (your old previous.js in this case) and rename it to sessionstore.js -- Windows should show it right next to sessionstore.old in alphabetical order

(4) Start Firefox and it should read sessionstore.js and restore whatever was in previous.js -- you might still need to check Recently Closed Windows for the missing window

Does that work for you?

About is a protocol, so you need to use a ":" as delimiter and not a ".": about:config

• http://kb.mozillazine.org/about:config

Yes, Restore remains unavailable. The explanation of how the files move around, taking new names, helps. I can do that.

Before I exit Firefox, now that I have about:config open is it safe to increase max_tabs_undo as well as max_windows_undo? Is there another setting that makes Firefox store more than one session?

It's safe to save more closed tabs and more closed windows, just don't go crazy with the values since this does increase the file size and time required to update the session history and incrementally increases the potential for corruption.

Firefox never saves more than one previous session. Over the years, the Session Manager extension was the best way to retain past sessions. From time to time users post panicked messages about how it stopped working after an update; I don't know the current status.

Thank you, all! I'll try the Exit and tell you in a few minutes whether it Restored properly.

It's all back! Thank you, Noah, Jscher, and Cor-El. I sure hope Firefox gets a decent built-in session restore procedure soon. A two-pane version of the "That's embarrassing" window would be a good model, with a control between the panes in case you want to scroll both in parallel while comparing the list of windows and tabs.

Thanks again, and good night.