Normally only tabs opened during the last 10 seconds are probably not yet saved to the sessionstore-backups folder. If is your case this happens with tabs that were opened 2 hours ago then it sounds that Firefox has a problem with saving the tab history.

Does Firefox create sessionstore files in the sessionstore-backups folder?

You can use this button to go to the current Firefox profile folder:

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Firefox uses the sessionstore.js file in the profile folder to store session data. The sessionstore.js file is only present when Firefox is closed. The sessionstore.js file is created from recovery.js when you close Firefox and is removed and copied to previous.js when you start Firefox to make is possible to restore the session at any time.

You will normally find these files in the sessionstore-backups folder:

previous.js (cleanBackup: copy of sessionstore.js from previous session that was loaded successfully)
recovery.js (latest version of the sessionstore written during runtime)
recovery.bak (previous version of the sessionstore written during runtime)
upgrade.js-<build_id> (backup created during an upgrade of Firefox)

You can copy a file from the sessionstore-backups folder to the main profile and rename the file to sessionstore.js to replace the current file (make a backup copy of the current sessionstore.js).

See also:

• http://www.ghacks.net/2014/06/27/mozilla-launches-improved-session-restore-firefox-33/

Thanks for the quick reply. Well, I can't read them (see attached error message - I guess, however, I'm not supposed to anyway. What puzzles me is, they are from yesterday 20:30. It's now 17:30. That's weird. I will now kill the task in the task manager and see if my tabs of this morning are still there. That's why I post now and let you know in a bit what happened.

Well, as expected - they're all gone. Ironically the session restore file recovery.js has now the date of when I terminated the task.

Hi Helen50, to view the contents of a .js file, don't double-click -- that executes the script. Instead, you can right-click > Edit the file, or open it using Firefox's Scratchpad tool.

Scratchpad

It's easiest if you've copied the .js file somewhere more easily navigable in Windows (e.g., Desktop, Documents).

Launch the Scratchpad from the Developer menu, either:

• "3-bar" menu button > Developer > Scratchpad
• (menu bar) Tools > Web Developer > Scratchpad

Use the Open button on the Scratchpad's toolbar to open the backup copy you made of recovery.js (or other session history file) and then click the Pretty Print button on the toolbar to re-layout the data in a more readable format.

You should find a list for each window that was open, and some that were recently closed, with tabs showing the last page and earlier history.

Note: you don't need to save the changes to the file when you close the Scratchpad unless you want to keep the "pretty" version for future reference.

Normally, the session history is updated as often as every 15 seconds, based on this preference you can find in about:config:

browser.sessionstore.interval => 15000

(It's in milliseconds, so 15000 = 15 seconds)

Even if you were to increase that to a minute (60000) or an hour (3600000), yours is much too far behind. It makes me wonder if the feature just stopped working for some reason.

THank you. Where do I find about:config:? It's not in the settings, help or command prompt.

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

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

• "about:" is a protocol to access special pages

Helen50 said

THank you. Where do I find about:config:? It's not in the settings, help or command prompt.

(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.

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

(3) Do any of these preferences have non-default ("user set") values? You can right-click > Copy and paste into a reply to get an opinion on whether it's a problem.

It is set to 15000. Do you have any ideas? It hasn't stopped entirely - only it does its job when it pleases. At the moment it's up to date 23:29. If I keep watching I might find a pattern but probably not. Thanks anyhow.