make showconfig -C /usr/ports/www/firefox
===> The following configuration options are available for firefox-43.0.4_1,1:
BUNDLED_CAIRO=on: Use bundled fork of cairo-1.9.5
CANBERRA=off: Sound theme alerts
DBUS=on: D-Bus IPC system support
DEBUG=off: Build with debugging support
DTRACE=off: Build with DTrace probes
FFMPEG=on: FFmpeg support (WMA, AIFF, AC3, APE...)
GCONF=off: GConf configuration backend support
GIO=on: Use GIO for file I/O
GNOMEUI=off: libgnomeui support module
INTEGER_SAMPLES=off: Integer audio sample format
LIBPROXY=off: Proxy support via libproxy
NVIDIA_GL=on: libGL support via nvidia-driver
OPTIMIZED_CFLAGS=on: Use extra compiler optimizations
PGO=off: Use Profile-Guided Optimization
PROFILE=off: Build with profiling support
TEST=off: Build and/or run tests
====> Options available for the multi AUDIO: you have to choose at least one of them
ALSA=on: ALSA audio architecture support
PULSEAUDIO=off: PulseAudio sound server support
====> Options available for the single TOOLKIT: you have to select exactly one of them
GTK2=on: GTK+ 2 GUI toolkit support
GTK3=off: GTK+ 3 GUI toolkit support
===> Use 'make config' to modify these settings