If you set Firefox to open a home page when it starts up, that should fix it. If you do not want to see a particular page as the home page, you can set that to about:blank. Do that at Options > General.

Make sure that Firefox closes properly and that there isn't a hanging Firefox or plugin-container process left in the task manager.

See:

• "Hang at exit": http://kb.mozillazine.org/Firefox_hangs
• "Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs

Use "Firefox/File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit") to close Firefox if you are currently doing that by clicking the close X on the title bar.

You can set the Integer pref browser.sessionstore.max_resumed_crashes to 0 on the about:config page to get the about:sessionrestore page immediately with the first restart after a crash has occurred or the Task Manager was used to close Firefox.

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

That way you see if a sessions has crashed or otherwise didn't close properly and will allow you to deselect the tab(s) that you do not want to reopen, but will allow to reopen other tabs.

@Finitarry: I already have a website set as my default (and startup) page. I have also tried to change and then return this option to no avail.

@Cor-el: FF is not crashing or hanging (tested using the max_resumed_crashes setting). Also, as per Task Manager, when I exit out of FF (using either the red 'x' in the upper right corner, or Firefox->Exit) the process closes down and ends entirely.

I'm sorry, folks, but neither of these proposed solutions did anything to help. FF still re-opens the last session even though all settings are telling it not to.

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

You can also try to reset Firefox:

• https://support.mozilla.org/kb/Basic+Troubleshooting

@Cor-el: I created a new profile and it no longer returned to the old session. Thank you. I even tried loading addons into FF to see if I could cause it to return to the problem and so far it has stopped entirely.

Using the instructions here: http://kb.mozillazine.org/Session_Restore#Disabling_crash_recovery

I was able to turn off that feature entirely without having to create a new profile.

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

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