why am I being signed out oof my sites that require a login overnight

I had the same thing happen to me, and for me it turned out to be the setting that deletes cookies and site data when Firefox closes. I found it under Privacy in the settings and turned it off, and after that my logins stayed put overnight. It is worth checking whether anything on your computer is clearing cookies overnight too, since I once had a cleaner app doing the same thing without me realizing it.