firefox-esr binaries provided in the universe repo
Like with ungoogled-chromium, firefox-esr is now officially in the Universe repo. You need to add the following to your /etc/pacman.conf
[universe]
Server = https://universe.artixlinux.org/$arch
For the curious, yes the build is exactly the same as the firefox-esr AUR package so it's an optimized build and has all the usual arch compile options.