No, that file has nothing to do with a browser session. Only compressed .jsonlz4 files in the sessionstore-backups folder could possibly restore an older session.

If you use the Time Machine or other backup then try to restore the sessionstore.jsonlz4 file(s) from this backup.

• https://support.apple.com/guide/mac-help/restore-files-mh11422/mac

You can 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 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

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)

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 with Firefox closed.

• make sure to backup the current sessionstore.jsonlz4

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

Thanks! I use Passport as a backup drive. When I look at the back ups from Passport unfortunately it doesn't look like it copied files from the hidden Library folder! Boo hoo. When I look at my hard drive shouldn't there be a .jsonlz4 for every session? I don't see one for the session on May 13th.

Thanks! Alice

When I look at my hard drive shouldn't there be a .jsonlz4 for every session? I don't see one for the session on May 13th.

Hi Alice, except when it updates, Firefox only stores ONE old session alongside the current session. If it stored ALL sessions indefinitely, that would be a lot of (personal) data.

If you are looking in the sessionstore-backups folder, the kinds of files you may find are:

• recovery.jsonlz4: the windows and tabs in your currently live Firefox session (or, if Firefox crashed at the last shutdown and is still closed, your last session)
• recovery.baklz4: a backup copy of recovery.jsonlz4
• previous.jsonlz4: the windows and tabs in your last Firefox session
• upgrade.jsonlz4-build_id: the windows and tabs in the Firefox session that was live at the time of your last update (and a few before, usually)

If you need to save more sessions on a regular basis, you'll need to use an add-on. I haven't tested these recently, but my list of what was available 18 months ago is as follows:

Add-ons that use database storage:

• https://addons.mozilla.org/firefox/addon/tab-session-manager/
• https://addons.mozilla.org/firefox/addon/session-boss/

Add-ons that use bookmark storage:

• https://addons.mozilla.org/firefox/addon/session-sync/
• https://addons.mozilla.org/firefox/addon/my-sessions/

(Bookmark storage is more robust in that Firefox backs it up regularly. However, having the extra data show up when you are searching your bookmarks may be annoying.)