Firefox-esr seems to be much more common (~118k): https://qa.debian.org/popcon.php?package=firefox-esr

Besides the point already made about firefox-esr being the default package for Firefox, here are a couple of other points. First, that also means there are 5749 installations of non-default Firefox compared to 231 of guix.

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.

That is still more than an order of magnitude higher (2.17% rather than 0.09%).

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.

It lists 118698 installs of firefox-esr.

https://qa.debian.org/popcon.php?package=firefox-esr