You may have corrupt sessionstore file(s). Delete all sessionstore* files and the sessionstore-backups folder.

Type about:support in the address bar and press enter.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the above. Then rename or delete them. Restart Firefox.

I already tried this, as I mentioned in passing above. I deleted all files with 'sessionstore' phrase in them as well as everything in the backup folder. I then restarted and it didnt work. I deleted the files and uninstalled. That didnt work either. I keep getting 3 month old tabs restoring when I open new window.

{ Ctrl + N } will open the Homepage, but I wonder if you have "Show my windows and tabs from last time" selected in Options; then as Fred mentioned, you have corrupt a sessionstore that has those old tabs?

Another possibility is that Sync has corrupt data and that old session is continually being "synchronized" back to that device. Reset your Firefox Account Password to clear your data from the Sync server, than as each device is re-connected to Sync you should have "clean" data being synchronized.

I did have "Show my windows and tabs from last time" selected but it's not restoring the previous session's tabs. It's restoring tabs closed down a very very long time ago.

I unlinked Sync before I went through the sessionstore files. Also, because I had forgotten my Sync password, I reset the password unintendedly. That didn't help either. After I reset the Sync password, ctrl+n still loaded the ancient tabs on the new window.

The problem is solved now because I uninstalled FF and then manually deleted all files anywhere in the Windows folders that were remotely linked to Mozilla. If I screwed something up, I don't yet know it but this problem was driving me crazy. I do think there must be a different and safer way to get rid of the issue.

Anyway, thanks for your suggestions and help.

That was very good work. Well done.

Did you remove only the files in the Programs Folder, or did you also remove the profile folder?

I deleted the profile folder.