Exactly, one way would be for @purismforum to follow and adjust things that are required/necessary as described within this link, for example within its sources.list to something like:
deb https://ftp.debian.org/debian/ sid main
Second “firefox” option would be to perhaps accept and go with proposal I posted earlier (and tell us if it works for him): L14 and new to linux - #34 by Quarnero. Related link is here: Installation on Debian based systems – LibreWolf.