The various Mozbase packages are used in mozilla-central python code; see https://developer.mozilla.org/en-US/docs/Python#Python_in_Mozilla-Central . Mozbase is used extensively throughout mozilla-central, including test harnesses, tools and the build system itself.
==== Adding new Packages ====
If you are adding a new package to mozbase, there are unfortunately three files you'll need to update in addition to your added files. Those are: