Notes on WHERE firefox dependencies are listed (to check minimum
versions), current as of firefox-113.0b3 :

libpng	media/libpng/png.h

libvpx	media/libvpx/libvpx/CHANGELOG

nss	security/nss/TAG-INFO
      security/nss/lib/nss/nss.h

nspr	security/nss/automation/release/nspr-version.txt
	nsprpub/pr/include/prinit.h
	(they have been known to get out of sync)

icu	intl/icu/GIT-INFO
	intl/icu/source/configure PACKAGE_VERSION
	js/moz.configure  ()test for icu-i18n)

libwebp	media/libwebp/MOZCHANGES
   With their use of automated updates they seem to leave this
   file alone.

node.js	NODE_MIN_VERSION from
	python/mozbuild/mozbuild/nodeutil.py
   In practice, this is ancient but allows old CI build bots.

cbindgen  cbindgen_min_versio from
	build/moz.configure/bindgen.configure

rust	MINIMUM_RUST_VERSION from
	python/mozboot/mozboot/util.py

Please note that build/defines.sh may define
	EARLY_BETA_OR_EARLIER - if so, needs a static libstdc++
	and attempts to include you in telemetry options.