This is Debian packaging for GNU IceCat. The latest release version of GNU IceCat is based on the outdated Firefox 60.7.0 ESR release, these builds are instead built from the latest commits from the GNU IceCat git repository at https://git.savannah.gnu.org/cgit/gnuzilla.git which follow the latest Firefox ESR releases.
Builds are available on OBS at https://build.opensuse.org/package/show/home:losuler:icecat/icecat.
This repo can be added on Debian 11 for example by (see here for examples for other Debian releases):
echo 'deb https://download.opensuse.org/repositories/home:/losuler:/icecat/Debian_11/ /' | sudo tee /etc/apt/sources.list.d/home:losuler:icecat.list
curl -fsSL https://download.opensuse.org/repositories/home:losuler:icecat/Debian_11/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/home_losuler_icecat.gpg > /dev/null