Thomas Abeel

This tutorials shows how to restore all tabs that were open when you closed Firefox.

Go to about:config, this should be typed in the address bar.
Go to the section with that starts with browser.sessionstore and set the values to the whatever you like.

browser.sessionstore.enabled (bool) - Activate the service. Default is true.

browser.sessionstore.resume_from_crash (bool) - Resume sessions post-crash. Default is true.

browser.sessionstore.resume_session_once (bool) - Resume session at the next application start, but not again. Default is false. This is used for restarting the browser after application updates and extension installation.

browser.startup.page (int) - What is displayed when Firefox starts: 0 = blank page; 1 = homepage; 3 = previous session (this is what you probably want if you're reading this). Default is 1. (Note: This preference is exposed in the Startup section of the Main pane of the Options/Preferences dialog.)