Add repository to sources.list:
deb http://ftp.us.debian.org/debian/ sid main deb-src http://ftp.us.debian.org/debian/ sid main
# Pinning setup for firefox: # ========================== # 1. Review the files in /etc/apt/preferences.d: # Pin-Priority should be: unstable<testing<stable<Debian Security # 2. Review and copy this file to /etc/apt/preferences.d # 3. Update system, no new packages should be installed!!! # # apt update # # apt upgrade << No new packages, otherwise pinning is wrong. ABORT!!! # 4. if all was ok above # # apt install -t sid firefox # Ref: https://linuxconfig.org/how-to-install-firefox-quantum-on-debian-stretch-linux # Package: firefox Pin: release a=unstable Pin-Priority: 1001 Package: libfontconfig1 Pin: release a=unstable Pin-Priority: 1001 Package: fontconfig-config Pin: release a=unstable Pin-Priority: 1001 Package: libnss3 Pin: release a=unstable Pin-Priority: 1001
Ref: https://linuxconfig.org/how-to-install-firefox-quantum-on-debian-stretch-linux