That you for including your system information, it shows you have a user.js file. That's an optional settings file with Firefox checks when it starts up, and uses to override your previous session settings. Sometimes the command to restore the previous session is in this file. You can hunt it down and remove it by following the steps in this article: How to fix preferences that won't save.

Any luck?

The user.js file had a "restore previous session" or wording to that effect in it. In fact that was the only line there. Deleted that line, saved the file. It works. Thanks, I appreciate it.