Sorry to hear that. Could you back up a few files: You can open your current Firefox settings (AKA Firefox profile) folder using either * "3-bar" menu button > "?" button > Troubleshooting Information * (menu bar) Help > Troubleshooting Information * type or paste about:support in the address bar and press Enter In the first table on the page, click the "Show in Finder" button. In your profile folder, scroll down and double-click into the '''sessionstore-backups''' folder. Save all files here to a safe location, such as your Documents folder. If not too much time has passed, we may be able to use them to recover your lost tabs. The kinds of files you may find among your sessionstore files are: * recovery.js: the windows and tabs in your currently live Firefox session (or, if Firefox crashed at the last shutdown and is still closed, your last session) * recovery.bak: a backup copy of recovery.js * previous.js: the windows and tabs in your last Firefox session * upgrade.js-''build_id'': the windows and tabs in the Firefox session that was live at the time of your last update Could you take a look at what you have and the date/time of the various files to see whether you think any of them would have the missing tabs? To view the contents of a session history file, you can drop it onto this page: https://www.jeffersonscher.com/res/scrounger.html (That's on my website, so if it doesn't seem to work correctly, please let me know.) ---- In addition to that "live" location, in case your Firefox performed a Refresh, could you check your Mac desktop for a folder named Old Firefox Data? If you have one, click inside and check around for other session history files, including possibly sessionstore.js in the folder one level up from sessionstore-backups.