To obtain the source code using git, you can clone the github repository by using the following command -
git clone git://github.com/gpgauth/gpgauth-npapi.git
Or you can fork the repository on the github.com website (https://github.com/gpgauth/gpgauth-npapi)
Once you have a local copy of the git repository, you will need to update the firebreath submodule by using this command in the directory that you have cloned the gpgauth-npapi repository to:
git submodule update --recursive --init
(Eventually I will make some build scripts that will negate the need to do this.)