Don't exit out of Firefox! Could you try backing up all your existing session history files. Here's how: 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. This should launch a new window listing all your settings files. Scroll down and copy all the file starting with sessionstore to a safe location for possible future recovery. ---- When you say you hit restart, do you mean quitting Firefox and starting it up again, or using the Reset feature? The Reset feature creates a folder on your desktop named Old Firefox Data, so if you find one, that would be a strong indication that a Reset was run at some point.