Were those tab the only data you lost? *https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-firefox-update You can check if you have an upgrade.jsonlz4 with those lost tabs. 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. *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 try to restore the upgrade.jsonlz4 file from the last update or use a utility to browse Windows System Restore points to see if you can find a recent sessionstore.jsonlz4 file. You can copy a file with Firefox closed from the sessionstore-backups folder to the main profile folder and rename the file to sessionstore.jsonlz4 to replace the current file. *make sure to backup the current sessionstore.jsonlz4 You can look at this tool to inspect a compressed jsonlz4 sessionstore file. This tool works locally, no uploading done. *https://www.jeffersonscher.com/res/scrounger.html