You can try to restore a recent upgrade.jsonlz4-<build_id> when available or use a utility to browse Windows System Restore points to see if you can find a recent sessionstore.jsonlz4 file.

You can look at this tool to inspect a compressed jsonlz4 sessionstore file.

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

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

• previous.jsonlz4 (cleanBackup: copy of sessionstore.jsonlz4 from previous session that was loaded successfully)
• recovery.jsonlz4 (latest version of sessionstore.jsonlz4 written during runtime)
• recovery.baklz4 (previous version of sessionstore.jsonlz4 written during runtime)
• upgrade.jsonlz4-<build_id> (backup created during an upgrade of Firefox)

With Firefox closed you can copy a file from the sessionstore-backups folder to the main profile and rename the file to sessionstore.jsonlz4 to replace the current file.

• make sure to backup the current sessionstore.jsonlz4

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

I'm sorry, I'm sure you are right but I don't understand anything of that :( :(

You can try to restore a recent upgrade.jsonlz4-<build_id> when available or use a utility to browse Windows System Restore points to see if you can find a recent sessionstore.jsonlz4 file. You can look at this tool to inspect a compressed jsonlz4 sessionstore file.

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

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

• previous.jsonlz4 (cleanBackup: copy of sessionstore.jsonlz4 from previous session that was loaded successfully)
• recovery.jsonlz4 (latest version of sessionstore.jsonlz4 written during runtime)
• recovery.baklz4 (previous version of sessionstore.jsonlz4 written during runtime)
• upgrade.jsonlz4-<build_id> (backup created during an upgrade of Firefox)

With Firefox closed you can copy a file from the sessionstore-backups folder to the main profile and rename the file to sessionstore.jsonlz4 to replace the current file.

• make sure to backup the current sessionstore.jsonlz4

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

I didn't understand what to do with any of this either and I'm very technical. Can you please provide a more comprehensive set of instructions? I can't tell how to open any of these things to see if they are the lost history window and merely open it ... not just view it. I can't read Firefox code with no primer.

I'm sorry, I'm sure you are right but I don't understand anything of that :( :(

Uh oh, I put a response in here to that contributor, but it never showed up. I can't tell what to do with any of that either and I'm fairly technical. Without a primer, regular users can't read Firefox code. Can cor-el please provide a more comprehensive set of instructions? I can't read Firefox code, so the tool does me little good to see if that's the lost window with many tabs.

It happened to me again for no reason other than I closed a window. 2 other windows were open, but I closed all of them before I went to sleep. Woke up and only 2 of the 3 opened and the 3rd window was gone from history. This is just a disaster to me and has there been a limitation on the # of windows (with multiple tabs) allowed to be open? Seems like 3 is the limit, but I'm afraid to have any more open than that. I can't be chasing down window tabs that I've had open for a few months.

Dang, I realize what happened to my response. I checked that silly box saying "I am providing the requested information". Sorry about that; I wasn't.

You can try to restore a recent upgrade.jsonlz4-<build_id> when available or use a utility to browse Windows System Restore points to see if you can find a recent sessionstore.jsonlz4 file. You can look at this tool to inspect a compressed jsonlz4 sessionstore file.

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

I responded to the poster, but was talking to you, @cor-el. How do we open sessionstore.jsonlz4 with Firefox? The tool doesn't restore them to Firefox. Is it a matter of figuring out what you said and renaming files?

Your first reply contained an external link and such a reply requires moderator approval. You should now see this reply, so no need to repeat.

Your first reply contained an external link and such a reply requires moderator approval. You should now see this reply, so no need to repeat.

Okay. Sorry about that @cor-el.

I figured it out per your instructions. annaxt probably isn't used to looking at files on his computer, or even how to open the profile folder. Open the application menu (3 horizontal lines) next to the address bar. Click on Help -> More troubleshooting information. With that page open, find Profile Folder and click on Open Folder. That's how you get to the folder with backup files in it, @annaxt.

I also set my computer up to see all the extensions & system files. By default, the extensions don't show up (.jsonlz4 is an extension). I found an older file in that sessionstore-backups folder and copied it one level back to the main profile folder. Renamed the sessionstore.jsonlz4 to sessionstore.jsonlz4.old and the file I copied, I renamed to sessionstore.jsonlz4. Opened Firefox and that missing window was in the history so I could open it. Don't make any typos here, because Firefox won't find the files it needs to open.

It doesn't have all the tabs I had open yesterday, but it was better than losing the entire window. I've lost windows when Firefox updates, too, but now I know how to find older files. Too bad there isn't a file with more recent history, but it'll do for now. Thanks.

Thank you @King Ray, I'm in the middle of moving house this week but as soon as I'm installed in the new place (and have found all necessary cables again!) I will try as per your instructions!