$ emerge -p firefox

These are the packages that would be merged, in order:

Calculating dependencies            ... done!                
[ebuild   R    ] www-client/firefox-65.0::gentoo  USE="-bindist clang -custom-cflags -custom-optimization dbus -debug -eme-free -geckodriver gmp-autoupdate -hardened -hwaccel -jack lto (-neon) -pgo pulseaudio screenshot (-selinux) startup-notification system-harfbuzz system-icu system-jpeg system-libevent system-libvpx system-sqlite system-webp -test -wayland -wifi" L10N="-ach -af -an -ar -as -ast -az -bg -bn-BD -bn-IN -br -bs -ca -cak -cs -cy -da -de -dsb -el -en-GB -en-ZA -eo -es-AR -es-CL -es-ES -es-MX -et -eu -fa -ff -fi -fr -fy -ga -gd -gl -gn -gu -he -hi -hr -hsb -hu -hy -id -is -it -ja -ka -kab -kk -km -kn -ko -lij -lt -lv -mai -mk -ml -mr -ms -nb -nl -nn -or -pa -pl -pt-BR -pt-PT -rm -ro -ru -si -sk -sl -son -sq -sr -sv -ta -te -th -tr -uk -uz -vi -xh -zh-CN -zh-TW" 0 KiB

Total: 1 package (1 reinstall), Size of downloads: 0 KiB

!!! The following update(s) have been skipped due to unsatisfied dependencies
!!! triggered by backtracking:

www-client/firefox:0


~ $ emerge -p firefox

These are the packages that would be merged, in order:

Calculating dependencies               ... done!              
[ebuild     U  ] www-client/firefox-65.0-r1::gentoo [65.0::gentoo] USE="-bindist clang -custom-cflags -custom-optimization dbus -debug -eme-free -geckodriver gmp-autoupdate -hardened -hwaccel -jack lto (-neon) -pgo pulseaudio screenshot (-selinux) startup-notification system-harfbuzz system-icu system-jpeg system-libevent -system-libvpx* system-sqlite system-webp -test -wayland -wifi" CPU_FLAGS_X86="avx2%*" L10N="-ach -af -an -ar -as -ast -az -bg -bn-BD -bn-IN -br -bs -ca -cak -cs -cy -da -de -dsb -el -en-GB -en-ZA -eo -es-AR -es-CL -es-ES -es-MX -et -eu -fa -ff -fi -fr -fy -ga -gd -gl -gn -gu -he -hi -hr -hsb -hu -hy -id -is -it -ja -ka -kab -kk -km -kn -ko -lij -lt -lv -mai -mk -ml -mr -ms -nb -nl -nn -or -pa -pl -pt-BR -pt-PT -rm -ro -ru -si -sk -sl -son -sq -sr -sv -ta -te -th -tr -uk -uz -vi -xh -zh-CN -zh-TW" 0 KiB

Total: 1 package (1 upgrade), Size of downloads: 0 KiB