You can backup the sessionstore.js file in the profile 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

See also:

• https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them
• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox

Firefox uses the sessionstore.js file in the profile folder to store session data, but this 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.

Backup the session files in the sessionstore-backups folder in the Firefox Profile Folder to make sure not to lose possible important session data. Do NOT close Firefox when Firefox is already running.

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/

Not sure about the paragraph:

Backup the session files in the sessionstore-backups folder in the Firefox Profile Folder to make sure not to lose possible important session data. Do NOT close Firefox when Firefox is already running.

Of course you can only close Firefox if it is (already) running.

Without closing Firefox, which file is the most up-to-date representation of my tabs? Is this recovery.js and is it written continually?

Or will I only get this latest tab data from closing Firefox? And is this always sessionstore.js for the latest?

Is the profile always in the same directory: C:\Users\MyName\AppData\Roaming\Mozilla\Firefox\Profiles\{arbitrary_8_characters}.default ? Or do these arbitrary values change, and how often?

Backup the session files in the sessionstore-backups folder in the Firefox Profile Folder to make sure not to lose possible important session data. Do NOT close Firefox when Firefox is already running.

This step would only be needed in case you are troubleshooting issues with session restore to prevent losing data in the sessionstore-backups folder when you would restart Firefox. I posted that part in my reply to provide some information about how session restore works.

The sessionstore.js files stores data of all open and closed tabs including pinned tabs, so if you have a backup copy of this file then you can restore the session stored in this file.

If you have submitted crash reports then please post the IDs of one or more recent crash reports that start with "bp-".

• bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

You can find the report ID of recent crash reports on the "Help -> Troubleshooting Information" page (about:support).

• click the "All Crash Reports" button on this page to open the about:crashes page and see all crash reports.

Alternatively you can open about:crashes via the location/address bar.

See also:

• http://kb.mozillazine.org/Mozilla_Crash_Reporter
• https://support.mozilla.org/kb/Mozilla+Crash+Reporter

Yes, interesting. The one most critical report-worthy crash was not submitted.

cdbf5c0d-93bd-4477-a50a-de38e463c264

Says it was withheld as a means of throttling information.

Oh, it seems to have submitted itself now that I expressed interest, old name is gone, new one with later date has appeared.

bp-51bb76e2-66f2-4130-bebb-e3dd22160716

KRS03 said

Without closing Firefox, which file is the most up-to-date representation of my tabs? Is this recovery.js and is it written continually?

The file is updated as often as every 15 seconds. It is removed if Firefox shuts down normally, and its contents can then be found in a sessionstore.js file.

Is the profile always in the same directory: C:\Users\MyName\AppData\Roaming\Mozilla\Firefox\Profiles\{arbitrary_8_characters}.default ? Or do these arbitrary values change, and how often?

The profile folder name does not change. That would cause chaos...

The crash report is a problem with the Shockwave Flash plugin.

• Process Type plugin Shockwave Flash Version: 22.0.0.209 Filename: NPSWF32_22_0_0_209.dll

The current SWF release is 22.0.0.210 that has been released a few days ago.

• https://helpx.adobe.com/content/help/en/security/products/flash-player/apsb16-25.html

You can find the latest Flash player versions for Firefox on this page:

• https://www.adobe.com/products/flashplayer/distribution3.html
• https://get.adobe.com/flashplayer/otherversions/

You can check for problems with current Shockwave Flash plugin versions and hardware acceleration in Firefox and try this:

• make sure you have the latest Flash version:
  http://www.adobe.com/special/products/flashplayer/fp_distribution3.html
• check for updates for your graphics drive drivers
  https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration
• disable protected mode in the Flash plugin (Windows Vista and later)
  https://support.mozilla.org/kb/adobe-flash-protected-mode-firefox
• disable hardware acceleration in the Flash plugin
  https://helpx.adobe.com/flash-player/kb/video-playback-issues.html
• disable hardware acceleration in Firefox
  https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

See also:

• http://kb.mozillazine.org/Flash#Troubleshooting