Firefox: Restore a Lost or Discarded Session

Problem:
If Firefox was not closed properly, it would show a restore previous session option. If you missed that option, or you changed your mind after starting a new session, there is still hope to restore your previous session.


To restore a previous session:
1. browse to %AppData%\Mozilla\Firefox\Profiles
2. select your profile, e.g. xxxxxxxx.default
3. make a backup copy of sessionstore.bak and sessionstore.js
4. close Firefox (if you haven't already)
5. delete sessionstore.js
6. rename sessionstore.bak to sessionstore.js
7. launch Firefox


Ref:
Restore a Lost or Discarded Firefox Session in Three Quick Steps