The script output will tell you where the SRPM is. Copy it somewhere else, or mock will delete it. Then build the SRPM into an RPM:
run mock --rebuild /path/to/srpm
== Other Dependencies ==
If your package depends on other mozilla-specific packages, I'm not sure what the best way to build is. The less-than-awesome technique I used was to hack /etc/mock/epel-6-x86_64.cfg to include pointers to the public mirrors of the puppetagain repos.
= Testing =