cat ->> /etc/portage/env/fffaster.conf <<'EOF'
CORES="2"
#FLAGS_BROKEN="-fno-unswitch-loops -fno-tree-loop-im"

FLAGS_LTO="-flto=${CORES}"
FLAGS_FFFAST="-O3 ${FLAGS_LTO} ${FLAGS_BROKEN}"

CFLAGS="${CFLAGS} ${FLAGS_FFFAST}"
CXXFLAGS="${CXXFLAGS} ${FLAGS_FFFAST}"
LDFLAGS="${LDFLAGS} ${FLAGS_LTO}"

AR="gcc-ar"
NM="gcc-nm"
RANLIB="gcc-ranlib"
EOF

cat ->> /etc/portage/env/nosandbox.conf <<'EOF'
FEATURES="-sandbox -usersandbox"
EOF

cat ->> /etc/portage/package.env/fffaster.env <<'EOF'
www-client/firefox      nosandbox.conf fffaster.conf
EOF

cat ->> /etc/portage/bashrc <<'EOF'
# export I_KNOW_WHAT_I_AM_DOING="no"

if [ "${EBUILD_PHASE}" == "postinst" ]; then
    if [ -n "${_GENERATING_PROFILE_ROOT}" ]; then
        install -o portage -g portage "${_GENERATING_PROFILE_ROOT}/.is_generated"
    fi
    if [ -n "${_COMPILING_PROFILE_ROOT}" ]; then
        install -o portage -g portage "${_COMPILING_PROFILE_ROOT}/.is_compiled"
    fi
fi
EOF

cat ->> /etc/portage/env/profile.run <<'EOF'
if ! echo "${CFLAGS} ${CXXFLAGS} ${LDFLAGS}" | \
   grep -E '\-f(no\-)?profile' >/dev/null; then

    FEATURES="-usersandbox"  # does not work

    PROFILE_ROOT="/etc/portage/env/profiles/${PN}/${PVR}"
    PROFILE_SUFFIX="_e1/_e2/_e3"
    PROFILE_DIR="${PROFILE_ROOT}/${PROFILE_SUFFIX}"

    PROFILE_USE="-fprofile-dir=\"${PROFILE_DIR}\" -fprofile-use -fprofile-correction"
    PROFILE_GEN="-fprofile-dir=\"${PROFILE_DIR}\" -fprofile-generate -fno-lto"
    # ^ saves bugs and memory (4.9.1)
    # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45375#c31

    if [ ! -d "${PROFILE_DIR}" ]; then
        mkdir -p "${PROFILE_DIR}"
    fi

    if [ -e "${PROFILE_ROOT}/.is_generated" ]; then
        chown -R root:root "${PROFILE_ROOT}"
        chmod -R ug+rw,o-w+r "${PROFILE_ROOT}"

        export _COMPILING_PROFILE_ROOT="${PROFILE_ROOT}"
        CFLAGS="${CFLAGS} ${PROFILE_USE}"
        CXXFLAGS="${CXXFLAGS} ${PROFILE_USE}"
        LDFLAGS="${LDFLAGS} ${PROFILE_USE}"
    else
        chown -R portage:users "${PROFILE_ROOT}"
        chmod -R ug+rw,o-rwx "${PROFILE_ROOT}"

        export _GENERATING_PROFILE_ROOT="${PROFILE_ROOT}"
        CFLAGS="${CFLAGS} ${PROFILE_GEN}"
        CXXFLAGS="${CXXFLAGS} ${PROFILE_GEN}"
        LDFLAGS="${LDFLAGS} ${PROFILE_GEN}"
    fi
fi
EOF

chmod +x /etc/portage/env/profile.run
mkdir -p /etc/portage/env/www-client/
ln -s /etc/portage/env/profile.run /etc/portage/env/www-client/firefox

emerge -1v firefox

# use firefox for a while, it will be slow as hell, then
# emerge -1v firefox again