How to edit `postgresql.conf` with pgAdmin 3?

Question

How does one edit the 'postgresql.conf' file with the pgAdmin app?

With pgAdmin 1.18.1 on Postgres 9.3.x, when I choose File > Open postgresql.conf I get a file picker dialog. And, yes, I'm connected in pgAdmin as the superuser 'postgres'.

I know I've done this in older versions of Postgres.