and we can't use autoconf 2.69 from core:
```
Generating /private/tmp/__UNKNOWN__-d0KV/mozilla-beta/configure using autoconf
cd /private/tmp/__UNKNOWN__-d0KV/mozilla-beta; /usr/local/Cellar/autoconf/2.69/bin/autoconf
build/autoconf/acwinpaths.m4:10: error: defn: undefined macro: AC_OUTPUT_FILES
build/autoconf/acwinpaths.m4:10: the top level
autom4te: /usr/bin/m4 failed with exit status: 1
make[1]: *** [/private/tmp/__UNKNOWN__-d0KV/mozilla-beta/configure] Error 1
make: *** [build] Error 2
```