Hi, I have contacted the Contributor of that link. Please hang in there for a answer. Thanks.

You normally copy a file from the sessionstore-backups folder to the main profile folder and rename the file to sessionstore.jsonlz4 to make Firefox use the file. You need to do this with Firefox closed. Also do not forget to check "History -> Recently Closed Tabs/Windows" to see if there are missing window.

Here's a painfully long step-by-step if you're still working on this:

https://support.mozilla.org/questions/1211870#answer-1095531

Note: The scrounger will show you both open windows and closed windows. After you restore the session, if you don't see the tabs you want, make sure to check the History menu for closed windows you can re-open. Either:

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

cor-el said

You normally copy a file from the sessionstore-backups folder to the main profile folder and rename the file to sessionstore.jsonlz4 to make Firefox use the file. You need to do this with Firefox closed. Also do not forget to check "History -> Recently Closed Tabs/Windows" to see if there are missing window.

That worked - sort of.... It worked in the way that the current session did not reopen. What did reopen, after a LONG wait was one of my windows. Just one. The other two of the three could reopen from history menu. But still the two windows missing after update are still missing. Next I did the same with the file upgrade.jsonlz4-20180128191252 then I got into the session from that update.

I guess this all indicates that the previous.jsonlz4 is corrupted in some way. If I could merge those files, I'd actually get most of my tabs back. I'd like to add the two windows from 20180128 into the previous.jsonlz4. Then I would be able to find the few missing tabs from the history of previous.jsonlz4.

Is there a way to export / import windows with tabs? If so I could export the windows and tabs when running at the 20180128 session, revert to the "previous" session (the one where two windows are missing), then finally import the windows/tabs that was exported

You can use the tool to extract links from a sessionstore file.

• https://www.jeffersonscher.com/res/scrounger.html

Firefox's only built-in session restore mechanism is to read sessionstore.jsonlz4. There isn't any kind of import/export. There are extensions, but they use their own formats.

While it would be messy, there might be an editor which could allow you to join parts of different session history files.

Could you try something: increase the limit on closed windows that can be restored, since you need four (or five?) and only get two (or three?). That setting is here:

(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) Double-click the browser.sessionstore.max_windows_undo preference and enter 5 or a higher value, then click OK

After exiting out of Firefox, repeat the sessionstore.jsonlz4 swap and see whether you can restore more windows on the next startup.

I got this sorted out by installing Session Boss addon. Then saved the session from 20180128. Then I reverted to the 20180405 recovery session, and imported the missing windows saved by Session Boss.

After having Session Boss installed for a couple of hours I realize it has to be removed - it eats about 3MB of diskspace pr hour by making automatic very frequent sessionbackups, AND makes switching/closing/opening new tabs/windows slow. There's no setting to change the frequency or disable the autobackup, or make it overwrite older backups. Hence it just accumulates session data into one ever growing file.

Also I've figured out what went wrong with the update - when closing firefox, it managed to save the session while it was closing! So: close two windows - save - close reminding windows. I managed to replicated the problem by putting the cpu to work at 100% while closing firefox.