If you are on Mac OSX running Time Machine with a Backup External Drive try this: 1. Close Firefox. 2. Navigate on your Hard Drive to User/Library/Application Support/Firefox/Profiles/~Folder that will say 'default'~/sessionstore.js 3. Click on sessionstore.js 4. Enter Time Machine. 5. Navigate to a 'Safe Time' just before Firefox crashed and lost your Tabs (like an hour or two). 6. When Time Machine goes back to the selected time, making sure "sessionstore.js" is still highlighted, click RESTORE on bottom right of Time Machine window. 7. You`ll be asked by Time Machine to either replace, rename or keep both files and seeing as your present "sessionstore.js" has lost all your Tabs, you`ll want to simply REPLACE it with the Time Machine Backup File. 8. Re-Open Firefox and you`ll see that the RESTORE PREVIOUS SESSION option is restored, click and Voila!

Worked for me-THANK THE GODS for Time Machine!!