How are you closing Firefox? Are you shutting it down with Quit or the Close button? If you close it by forcing it to crash by turning off the computer without first exiting properly, it will return your last session when you start it up next.

hello, in past questions this has also been caused by a user.js file within the profile folder (which generally should only be present in case you have intentionally created it manually).

so please try the following: go to the firefox menu ≡ > help ? > troubleshooting information > profile folder - "show folder", then a new window will open up. in this window look out for a file named user.js (it might be used to overwrite your custom settings). in case it is present , delete or rename this file and restart firefox afterwards.

How to fix preferences that won't save

You can check if you have a user.js file in the Firefox profile folder that sets the browser.sessionstore.resume_session_once pref to true.

• http://kb.mozillazine.org/browser.sessionstore.resume_session_once