And FF ESR is the more common by far (44.5%) as it is the default, people only install the other FF package if they have specific need to be closer to the leading edge. The build environments for the two will be very close, at least compared to the oddities being reported in the Guix requirements, so the hassle of maintaining FF and FF-ESR compared to just one of them is not going to be comparatively large compared to maintaining packages for just one of the pair.
If more Guix users want to be seen and counted, to show how much of a need there might be to keep it despite the current issues, then there is a simple thing they can do… Or a less simple thing: the “without a community nor help” part seems rather significant to me in “But the Debian package maintainer has the almost impossible task to backport all the security fixes without a community nor help behind [maintaining it] and as things are going, this will probably lead to the Debian guix package being removed”.
Secondly, popcon works on servers and headless systems without X or Wayland. Those systems still use a package manager, and sometimes several. A graphical web browser like Firefox is unlikely to be installed without a GUI. I’ve seen plenty of systems with Snap, Flatpak, or Nix installed besides the OS-related apt, aptible, apt-get, rpm, yum, dnf, and language-related tools like pip, EasyInstall, rubygems, Bundler, cpanm, npm, cargo, OPAM, Composer, go get, or sbt with no GUI.