I've found my way. I clicked on the button "Profile Directory: Show in Finder" and up came a window with all those background Firefox files. I eliminated everything having to do with book marks and ePubs. Then I closed and reopened Firefox. The list of ePubs was gone. I opened my newest ePubs. #1 opened as expected. #'s 2-5 opened fine also. The one caveat, only #1 appears in the ePub list. This is because, I assume, they all have the same Identifier, so the first on eopen gets listed.
What have I learned? Many things, but not to use an existing ePub as a template for additional ePubs is the biggest lesson.
Thanks - Fabe