Firefox will restore your previous session at startup in three different situations:

(1) Startup setting changed to "Show my windows and tabs from last time"

You can check that using the steps in this article: Startup, home page, tabs, and download settings.

(2) Recovering from a crash, Firefox will try to restore your previous session. If Firefox shut down normally, then this probably isn't the cause.

(3) Preference override in the optional user.js settings file.

Some external software has been reported to set up an override so that you always get your previous session tabs instead of your home page. Your "More System Details" reports that you actually do have a user.js file in your active settings (profile) folder.

This article describes how to track down the user.js file and, assuming you didn't create it yourself, remove it: How to fix preferences that won't save. If you are using it for other purposes, you can delete the lines that don't belong.

Success?

Have you noticed any other strange symptoms?

Somewhere in the options->general there should be an option to let browser start with homepage instead of last visited page. Check it out.

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

Your System Details list shows that you have a user.js file in the profile folder to initialize prefs each time Firefox starts. The user.js file is only present if you or other software has created this file and normally it wouldn't be there.

You can check its content with a plain text editor (right-click: "Open with"; do not double-click). The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session.

You can delete the user.js file if you didn't create this file yourself.

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox