Please copy the source archive for the Mozilla sources into this directory.
At the moment "mozilla-source-1.7.5.tar.gz" is required, it can be found
here:
  http://ftp.mozilla.org/pub/mozilla.org/mozilla/releases/mozilla1.7.5/source/

Windows builders need also
  "vc71-glib-1.2.10-bin.zip" and
  "vc71-libIDL-0.6.8-bin.zip".
They can be found here:
  ftp://ftp.mozilla.org/pub/mozilla.org/mozilla/libraries/win32/

And also
  "wintools.zip"
which can be found here:
  http://ftp.mozilla.org/pub/mozilla.org/mozilla/source/wintools.zip