Hi Bill, could you check whether either of these have items:

• (menu bar) History > Recently Closed Windows (and within each restored window, Recently Closed Tabs)
• "Library" toolbar button > History > Recently Closed Windows (and within each restored window, Recently Closed Tabs)

If that doesn't help...

Firefox creates numerous session history files, but because session history is only for the immediately previous session, it is unfortunately too easy to lose it. Could you start by making a backup of your existing session history files? Here's how:

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

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Open Folder" (or "Show in Finder") button.

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

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
• upgrade.jsonlz4-build_id: the windows and tabs in the Firefox session that was live at the time of your last update
• various .js files from Firefox 55 or earlier

Could you take a look at what you have and the date/time of the various files to see whether you think any of them would have the missing tabs?

To preview the contents of a file, you can drag and drop it onto this page, then click Scrounge URLs: https://www.jeffersonscher.com/ffu/scrounger.html

That tool is on my site, so please let me know if it doesn't work for you.

Huge Thanks for the information and speedy reply, jscher2000.

I opened the sessionstore-backups folder, and copied the items to another folder for safety. The sessionstore-backups folder contained the following items; previous.jsonlz4, recovery.baklz4, recovery.jsonlz4, and upgrade.jsonlz4-20181018182531.

I dropped the previous.jsonlz4 file onto your absolutely AMAZING Session History Scrounger for Firefox utility, and it was able to recover every window and tab url from yesterday's session.

HUGE THANKS for that!!! Now I need to know how I can open a brand new Firefox session utilizing the information in that file to restore yesterday's session?

You can save the scrounged URLs as a safety...

To try swapping in a session history file from your backup folder so Firefox will load it, the standard "manual swap" method is as follows (assuming Firefox is still running):

(1) From inside Firefox, open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Show in Finder" button. This should launch a Finder window listing the various files and folders in your profile.

(2) Leaving that window open, switch back to Firefox and Quit, either:

• "3-bar" menu button > "power" button
• (menu bar) Firefox > Quit Firefox

Pause while Firefox finishes its cleanup -- these changes should occur:

• recovery.jsonlz4 is moved from the sessionstore-backups folder to the main level of the profile folder and renamed to sessionstore.jsonlz4
• recovery.baklz4 is deleted from sessionstore-backups

If that doesn't happen, you may need to hide the sessionstore-backups folder by renaming it to sessionstore-backupsOLD or similar.

(3) Once Firefox has stopped updating things, while viewing the main level of the profile folder, rename sessionstore.jsonlz4 to sessionstoreOLD.jsonlz4.

(4) Copy in the file you want to restore (for example, previous.jzonlz4), and rename it to sessionstore.jsonlz4 -- after the rename, Finder should show it right next to sessionstoreOLD.jsonlz4 in alphabetical order (if it works like Windows)

(5) Start Firefox and it should read the swapped in sessionstore.jsonlz4 and restore whatever was in the substitute file; if you do not have Firefox set to restore your previous windows and tabs automatically, use men > Restore Previous Session or (menu bar) History > Restore Previous Session

Any luck?

If you use the Time Machine or other backup then try to restore the sessionstore.jsonlz4 file from this backup.

• http://www.apple.com/support/timemachine/

Greetings jscher2000,

It took a while, but your patience and clear instructions helped me restore all of my missing windows and tabs.

I am incredibly thankful for your assistance, and have captured your instructions (attributing them with your name) to share with Family & Friends – should they encounter the same issues. (Or for me, should this ever happen again…)

Huge THANKS for your expertise. Wishing you a terrific weekend.

     Bill

Hi jscher2000,

Do you know of any browser extension that might automatically archive the previous day's session, allowing one to selectively go back one or several days to recall that day's complete history? Automation that might capture every open window and tab at a set time each day, and offer several days of selectable archives from which to restore (prior to purging the oldest off of the list).

Hi Bill, there are a number of session management add-ons, but I don't know whether any of them capture a time-based snapshot. You could take a look at:

• https://addons.mozilla.org/firefox/addon/tab-session-manager/
• https://addons.mozilla.org/firefox/addon/my-sessions/
• https://addons.mozilla.org/firefox/addon/session-boss/
• https://addons.mozilla.org/firefox/addon/session-sync/

Thank you. Have a terrific weekend.