Just happened to me in Waterfox, but I learned a few years ago how to get them back. I make copies of my '''sessionstore-backups''' folder because sometimes the files in the folder get reset and you lose your session. see screenshot Let's get to it... Post a screenshot of the files in your '''sessionstore-backups''' folder in your profile. see screenshot Here's info about the files in the folder. https://support.mozilla.org/en-US/questions/1415643 Here's more info from another user issue. https://support.mozilla.org/en-US/questions/1477659#answer-1713872