firebuild source code is hosted on GitHub. There are following repositories:
combust-labs/firebuild: the main repository containing the host targeting part of the system: linkcombust-labs/firebuild-mmds: the guest facing components used for the vminit binary: linkcombust-labs/firebuild-shared: shared components: gRPC driver and common structures: linkcombust-labs/dockerfiles: a set of Dockerfiles for some of the common infrastructure components: link