I also lost everything during an update and as for themes and extensions I do backup those from time to time since then. But losing tabs is a lot worse. At leas

I also lost everything during an update and as for themes and extensions I do backup those from time to time since then. But losing tabs is a lot worse. At least there's a way to get them back though - e.g. on windows it's %APPDATA%\Mozilla\Firefox\Profiles\your_profile\sessionstore-backups. After you close FF you can copy over the .jsonlz4 backup to your_profile and replace the sessionstore.jsonlz4 file.