As an add-on to the initial post, I also deleted the current sessionstore.jsonlz4 file and replaced it with previous.jsonlz4 but that also did not solve the problem. The last session is not available to be restored.

Hopefully you saved copies of all those different files?

You can drag-and-drop them onto this tool on my website and "Scrounge" the links to see which one is the best match to your lost tabs.

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

It could be the latest file whose name starts with

upgrade.jsonlz4-

since one of those should be created for each update (but the older ones are discarded later).

Once you know which file you want Firefox to use at startup:

(1) Exit Firefox and wait for it to create the sessionstore.jsonlz4 file in your profile folder (not the sessionstore-backups subfolder)

(2) right-click > Rename the sessionstore.jsonlz4 file in the profile folder to sessionstoreOLD.jsonlz4

(3) Copy the old file you want to use and paste it into the current profile folder (please don't move the original in case this takes multiple tries)

(4) right-click > Rename the old file to sessionstore.jsonlz4

If the old file does not already have "lz4" somewhere in its file extension, it may be from the Firefox 55 era. In that case, rename that file to sessionstore.js so Firefox knows it is not compressed

(5) right-click > Rename the sessionstore-backups folder to sessionstore-backupsOLD so Firefox doesn't try to use those files (it will create a new one)

(6) Start up Firefox

Success?

Hello jscher2000, and thanks for your help. I followed your instructions but unfortunately nothing changed - it does not open the previous tabs and there is no option available to restore the previous session.

Is Recently Closed Windows available? Either:

• (menu bar) History > Recently Closed Windows
• Library toolbar button > History > Recently Closed Windows

No, it is not available.

When you "scrounge" the file, are the tabs listed in the clickable results? If all else fails, you can save that page and relaunch the tabs that way.

Yes, the tabs are listed in the clickable results. Would I have to click them one at a time to reopen all?

Alwi said

Yes, the tabs are listed in the clickable results. Would I have to click them one at a time to reopen all?

Unless you have one of those add-ons where you select a part of a page and it opens all the links in that selection at once. To avoid your computer grinding to a halt, I wouldn't do more than 10 on the first try to see how it goes.

I don't have the add-on you mentioned, so I guess I will have to do this for each tab...Is there a way to avoid this from happening again?

Hi Alwi, you can look for add-ons on the Add-ons site:

https://addons.mozilla.org/en-US/firefox/extensions/

Is there a way to avoid this from happening again?

I don't think we've figured out what went wrong, so it's difficult to know whether that same situation might arise again. It's definitely not normal to lose your session history during an update; a session snapshot file is created to help protect against that.

Thank you for your help!

The same thing happened to me and in the update to 58.0.2 on Windows 7. The old sessionstore files which I was able to use to recover my tabs no longer work. I can view them in the Scrounger but it's too much to go through that way. Is it possible that this will be fixed in a future update?

bazpix said

The same thing happened to me and in the update to 58.0.2 on Windows 7. The old sessionstore files which I was able to use to recover my tabs no longer work. I can view them in the Scrounger but it's too much to go through that way. Is it possible that this will be fixed in a future update?

What do you mean by "no longer work" -- you tried the file swap (steps in my first reply) and Firefox didn't read the substitute file?

Regarding the future, the developers of session management extensions are pushing for changes, but I expect them to come slowly, so for the next several months, I don't expect the overall design of things to change.

Yes, I tried the file swap which was successful in restoring tabs for me in previous versions. Admittedly this was using a sessionstore.js file which I renamed as sessionstore.jsonlz4, but doing exactly that worked when I lost my tabs last month.

This time it reverted to the backup profile, with the tabs from my most recent session, instead of the profile I swapped in to replace the sessionstore.jsonlz4. When I removed the backup profiles from the folder they're stored in it loaded a new session with no tabs.

By way of follow up, I've now built up a number of tabs so I went to try and save the current sessionstore.jsonlz4 in case I lose them. I found that it's only 329kb and the backups are the same size. Yet when I restarted Firefox the tabs all loaded.

This file size seems too small to store all the tab information. Could there have been a change to how it's stored?

LZ4 is a compression algorithm. The uncompressed data is much, much larger. You can use the Scrounger page to save an uncompressed .json version of the data for comparison.