it comes from this check of mozilla-central/client.mk
# try to find autoconf 2.13 - discard errors from 'which'
# MacOS X 10.4 sends "no autoconf*" errors to stdout, discard those via grep
AUTOCONF ?= $(shell which autoconf-2.13 autoconf2.13 autoconf213 2>/dev/null | grep -v '^no autoconf' | head -1)
The autoconf in the Ubuntu desktop system is of version 2.69. It is clearly not compatible.