FIRST. Create a directory to store APT repository keys if it doesn’t exist:
sudo install -d -m 0755 /etc/apt/keyrings
SECOND. Import the Mozilla APT repository signing key:
wget -q https://packages.mozilla.org/apt/repo-signing-key.gpg -O- | sudo tee /etc/apt/keyrings/packages.mozilla.org.asc > /dev/null
THIRD. The fingerprint should be 35BAA0B33E9EB396F59CA838C0BA5CE6DC6315A3. You may check it with the following command:
gpg -n -q --import --import-options import-show /etc/apt/keyrings/packages.mozilla.org.asc | awk '/pub/{getline; gsub(/^ +| +$/,""); if($0 == "35BAA0B33E9EB396F59CA838C0BA5CE6DC6315A3") print "\nThe key fingerprint matches ("$0").\n"; else print "\nVerification failed: the fingerprint ("$0") does not match the expected one.\n"}'
FOURTH. add the Mozilla APT repository to your sources list:
echo "deb [signed-by=/etc/apt/keyrings/packages.mozilla.org.asc] https://packages.mozilla.org/apt mozilla main" | sudo tee -a /etc/apt/sources.list.d/mozilla.list > /dev/null
FIFTH. Configure APT to prioritize packages from the Mozilla repository:
echo ' Package: * Pin: origin packages.mozilla.org Pin-Priority: 1000 ' | sudo tee /etc/apt/preferences.d/mozilla
SIXTH. Update your package list and install the Firefox .deb package:
sudo apt-get update && sudo apt-get install firefox-devedition