Could you check your profile for for any "extra" sessionstore files? Here's how: Open your current Firefox settings (AKA Firefox profile) folder using either * "3-bar" menu button > "?" button > Troubleshooting Information * Help menu > Troubleshooting Information In the first table on the page, click the "Show Folder" button Scroll down and look for sessionstore.js (which should have a very current timestamp) and sessionstore.bak (which should be dated as of your previous session). Do you find both of those? Do you find any extra files, such as sessionstore-1.js or other numbered files? If so, that indicates that Firefox cannot write to the main sessionstore.js file because it is locked or corrupted, as your windows/tabs are being saved in a different file. Unfortunately, Firefox can't actually restore any of those files automatically. In this situation, I believe you need to remove the sessionstore.js file (probably after exiting out of Firefox) and rename the current numbered file to sessionstore.js. ---- You mentioned that you checked your settings, and it didn't sound as though you had any questions about them. But... could you post your customized session history settings? Here's how: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter. Click the button promising to be careful. (2) In the search box above the list, type or paste '''sess''' and pause while the list is filtered (3) Review the preferences starting with: * browser.sessionhistory. * browser.sessionstore. If you see bolded entries, which indicates that they vary from the default setting, could you right-click > Copy and post in a reply to see whether they might be relevant to this problem?