Slow javascript .mozconfig

.mozconfig

# If ccache was installed via Homebrew:
export PATH="`brew --prefix ccache`/libexec:$PATH"

# Import the stock config for building the browser (Firefox)
. $topsrcdir/browser/config/mozconfig

. $topsrcdir/build/macosx/mozconfig.common

# Define where build files should go. This places them in the directory
# "obj-ff-dbg" under the current source directory
mk_add_options MOZ_OBJDIR=@TOPSRCDIR@/obj-ff-dbg

# -s makes builds quieter by default
# -j4 allows 4 tasks to run in parallel. Set the number to be the amount of
# cores in your machine. 4 is a good number.
mk_add_options MOZ_MAKE_FLAGS="-s -j4"

mk_add_options AUTOCONF=/usr/local/Cellar/autoconf213/2.13/bin/autoconf213