OpenBSD blobs

A while ago there was this topic:

https://trisquel.info/en/forum/libertybsd-openbsd-minus-blobs

I don't want to argue about the licenses. But about the technical aspect.

On libertybsd.net it says:

That this blobbed microcode/firmware is a problem for openness, that I can understand. There is no point having a super secure OS if the hardware is already compromised. No matter what OS.
http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sys/dev/microcode/

And this:
cvsweb.openbsd.org/cgi-bin/cvsweb/src/distrib/miniroot/install.sub.diff?r1=1.653&r2=1.654&f=h
"by default a script will download more at first boot, without informing the user of this."
Well what dos this code exactly do? "Update firmware"? I guess is updates to the latest firmware by downloading new firmware from the internet?
It doesn't exactly state -what- is downloaded and from -where-. Anybody knows?