I imagine the Firefox thing is to make the initial setup of a machine faster (doing Firefox addons and other packages in one shot with apt-get), and possibly be

I imagine the Firefox thing is to make the initial setup of a machine faster (doing Firefox addons and other packages in one shot with apt-get), and possibly because the maintainer's didn't trust the security of Firefox's update mechanism. If you can rely on apt-get always being available, you tend to use it as a first resort.