In terms of building it's almost exactly the same as for the 12-series: the only difference is that you have to build outside the source tree.
rm comm-release -rf
tar xvf thunderbird-13.0.source.tar.bz2
The next step takes a while (30-60 minutes)
sudo make install
No rule to make target ../../../xpcom/idl-parser/xpidllex.py
Build outside the source tree as shown above.