From the (10.3/unstable) .info, it appears that two copies of mozilla
source are downloaded. One is explicit in Source3, but PatchScript
appears to use one that's already one in the main (Source) tarball. Is
the one from Source3 ever actually used?
  
While on the topic, why do you need to compile your own mozilla at all
(the --enable-build-mozilla flag)? Fink has a mozilla package already;
using it would save many hours and many MB of disk space during the
oo.o compile. As a bonus, you get the advantage of many important
patches that are part of fink's mozilla.