When you shut your PC down without closing Firefox first, Firefox thinks it crashed and when you restart it the previous session is automatically restored. That is how Firefox is designed to work. Best the Exit Firefox before turning your PC off.

I shut down firefox before i shut off my pc

There is software like Advanced SystemCare with its Surfing Protection feature that can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

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

See also:

• http://kb.mozillazine.org/Preferences_not_saved

You can check for problems with the sessionstore.js file in the profile folder that stores session data. When sessionstore.js is deleted you lose pinned tabs and Tab Groups and open tabs and you will have to recreate them, so if necessary make a note or bookmark them.

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

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

One way to diagnose whether Firefox thinks it is crashing at shutdown is to set a different post-crash startup behavior. Rather than trying to restore automatically, Firefox will display a list of windows and tabs you had open before and ask whether you want to restore them or start a new session. Here's how you get to that, if you want to try it:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Double-click the browser.sessionstore.max_resumed_crashes preference and change its value from 1 to 0 (zero) and click OK

Please be careful not to change other session restore settings so that you can preserve this option for when you really need it.

I just remembered that last update firefox.exe kept running in the processes and that must've been what was making it think Firefox was still open while shutting down. After updating to the new version it hasn't happened.