Being unable to build Firefox on the Ubuntu machine in 202, I decided to try it
on my laptop.  I was able to download and clone (with mercurial) the repository
over night.

When I tried to run the makefile I got the error:

make -f /{path}/mozilla-central/client.mk realbuild
/{path}/mozilla-central/client.mk:281: *** Could not find autoconf 2.13.  Stop.

After a little googling I found this page:
https://developer.mozilla.org/En/SpiderMonkey/Build_Documentation

Though it didn't specifically describe my problem, it mentioned that I needed
autoconf version 2.13 and no later version would work. 'man autoconf' revealed
that the -V flag would print the version number then exit and 'autoconf -V'
revealed that I have version 2.68.

I found and downloaded the source for version 2.13.  I thought I might need the
new version for something else and I know theres a way to specifically point to
the old version within the mozilla-central directory.  The trouble is I'm not
sure what that would be called so I'm not sure how to google it.