all my tabs have disappeared.

Hello, Firstly, you can try restoring your previous tabs by going to menu > history > recently closed windows / recently closed tabs. If it doesn't work, then you can manually try restoring from a backup. To do this, press win + R, then type %APPDATA%\Mozilla\Firefox\Profiles, and hit enter, then open the sessionstore-backups folder, then find any files named recovery.jsonlz4/ previous.jsonlz4/ upgrade.jsonlz4, and copy this to your main profile folder, and replace the original file, then restart Firefox.