This is outdated. Mozilla has it's own APT repository now, even for stable (it used to be only for nightly+beta): <a href="https://support.mozilla.org/en-US/kb/install-firefox-linux#w_install-firefox-deb-package-for-debian-based-distributions" rel="nofollow">https://support.mozilla.org/en-US/kb/install-firefox-linux#w...</a>