Gentoo does it for firefox-bin:

/usr/portage/www-client/firefox-bin/firefox-bin-69.0.ebuild

    MOZ_HTTP_URI="https://archive.mozilla.org/pub/mozilla.org/${MOZ_PN}/releases/"
    ...
    SRC_URI="${SRC_URI}
        amd64? ( ${MOZ_HTTP_URI%/}/${MOZ_PV}/linux-x86_64/en-US/${MOZ_P}.tar.bz2 -> ${PN}_x86_64-${PV}.tar.bz2 )
        x86? ( ${MOZ_HTTP_URI%/}/${MOZ_PV}/linux-i686/en-US/${MOZ_P}.tar.bz2 -> ${PN}_i686-${PV}.tar.bz2 )"