Firefox would normally restore the tabs when restarting to apply an update. Were you using a Private Browsing mode session as in that case this will fail ? You can check whether an upgrade.jsonlz4 file got created in the sessionstore-backups folder that possibly has your lost tabs. You can use the button on the "Help -> More Troubleshooting Information" (about:support) to go to the current Firefox profile folder or use the <b>about:profiles</b> page (Root directory). *Help -> More Troubleshooting Information -> Profile Folder/Directory:<br>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 try to restore the upgrade.jsonlz4 file from the last update or if you use the Time Machine or another backup, check if you can find a recent sessionstore.jsonlz4 file. 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 You can copy a file from the sessionstore-backups folder with Firefox closed 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