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

Calculating dependencies... done!
[ebuild   R   ~] www-client/firefox-37.0.1-r99::hardened-development  USE="dbus jit minimal -bindist -custom-cflags -custom-optimization -debug -gmp-autoupdate -gstreamer (-hardened) (-pgo) -pulseaudio (-selinux) -startup-notification -system-cairo -system-icu -system-jpeg -system-libvpx -system-sqlite {-test} -wifi" LINGUAS="de -af -ar -as -ast -be -bg -bn_BD -bn_IN -br -bs -ca -cs -cy -da -el -en_GB -en_ZA -eo -es_AR -es_CL -es_ES -es_MX -et -eu -fa -fi -fr -fy_NL -ga_IE -gd -gl -gu_IN -he -hi_IN -hr -hu -hy_AM -id -is -it -ja -kk -km -kn -ko -lt -lv -mai -mk -ml -mr -nb_NO -nl -nn_NO -or -pa_IN -pl -pt_BR -pt_PT -rm -ro -ru -si -sk -sl -son -sq -sr -sv_SE -ta -te -th -tr -uk -vi -xh -zh_CN -zh_TW" 0 KiB

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