Firefox remembers up to three previously closed windows when you restore your previous session. You can find them through either:

• "3-bar" menu button > Library > History > Recently closed windows
• (menu bar) History > Recently closed windows
• Ctrl+Shift+n -- opens in reverse of the order they were closed, sort of like Undo last

Is three enough?

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar to ensure that all open windows can be reopened.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

Three is fine. I was caught by surprise, not aware I had more than one window open, bbc I was taking a test and the test opened several on its own. So I closed the main window and found several others open. Closed those (I think at that point the game was already up, I couldn't restore the main window) and found I couldn't restore anything.

I have the same problem. I've instructed Firefox to open new windows in tabs, but it doesn't always do that. Further, when I'm using my online e-mail, replies are in new "little windows" and when something sets dozens of cookies FF crashes. And there go all my tabs. Again. And no, three is not enough.

If you notice that there are other windows still open when you have closed the main window via the close X then reopen your main window (Ctrl+Shift+N).

• https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly

Hi nordvie, when Firefox crashes and does an automatic session restore at your next startup, all of the windows and tabs open at the time of the crash should be restored. There is no limit on the number of open windows and tabs that are restored. It sounds as though your Firefox is not doing a crash recovery, or that your Firefox might be set not to store session history.

It's spotty. Sometimes it does, sometimes not. Same thing when there's a power outage. Sometimes, despite my exiting step-by-step, I get just the last window (usually an empty e-mail response in progress if not just initial tabs. Where do I go, please, to be sure I've done everything possible to set it to store session history? Under Options, at General, I've set to Restore to previous session and at>History to use custom settings, and save Browsing and Download history. There's a button to "Clear History" but it doesn't appear to have settings available. I had when the new interface presented on update, temporarily checked Clear history when Firefox closes, and under the Settings Button unchecked Download & Browsing History, Active Logins and Offline Website Data, then "unchecked" the Clear History box. It'd be nice to have it clear everything else, but I hadn't time then to read up on it. It seems the last update might have re-set to a hard clear? It'd be nice to have a 1-step "Clear History" that would clear what I wanted it to, but otherwise honor the same settings as the "Clear when Firefox closes" but I wanted to avoid clearing anything in the event of a power outage. Should I be doing anything differently to have the session restore functionality as you've described"

Hi nordvie, Firefox has been much more sensitive to system/power out crashes recently. I think it started in Firefox 67, and some improvements hopefully were made for Firefox 68.

Sometimes, despite my exiting step-by-step, I get just the last window (usually an empty e-mail response in progress if not just initial tabs.

What do you mean by step-by-step?

Under options, with

Firefox will: Use custom settings for history

it's best NOT to check the box for "Clear history when Firefox closes" but if you do, the Settings button to the right will become enabled and you can make sure you aren't clearing Browsing & Download History. If you get any kind of recovery, this probably is fine.

To check your closed window recovery depth:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) The browser.sessionstore.max_windows_undo preference defaults to 3 but you can increase that if you like. Double-click and enter the new higher value then click OK.

By step-by-step, I mean closing any open windows but the main window. Those are usually e-mails in process, and their being restored with content depends on the e-mail server's being open ... which it can't be in a one-step restoration. So if they're important enough to not start over, I save them to .txt, and shut them down, till only the main window with its tabs is openj. Thanks so much for what you do!

Thanks tons! I only set the options for the Clear History when FF closes as double insurance, then unchecked the Clear History when... button before closing the tab in which I'd opened options. Here's hoping for next power outage! Thank you again.

nordvie said

By step-by-step, I mean closing any open windows but the main window. Those are usually e-mails in process, and their being restored with content depends on the e-mail server's being open ... which it can't be in a one-step restoration. So if they're important enough to not start over, I save them to .txt, and shut them down, till only the main window with its tabs is open.

By default, Firefox may take up to 15 seconds to update the recovery.jsonlz4 file, so if you are making a lot of changes quickly toward the end right before exiting, I think it's possible that some changes could get lost. But logically, that should leave more windows open, not fewer, so... hmm...

I agree. I'll be using the FF Exit command, and maybe that will help, at least for when we don't have a power outage. Back when, it worked then, too. I'd rather reconstruct tabs with history, though, than use Google product, So you folks have been a great help already! Thanks again.

See also this extension to inspect a compressed jsonlz4 file.

• mozlz4-edit
  https://addons.mozilla.org/firefox/addon/mozlz4-edit/