Tools:

Virtualbox for running Webconverger on your host system as a guest
Wireshark for packet sniffing

Tested in Windows. Unfortunately Virtualbox bridged networking under Linux tends to be broken.

Webconverger settings

most network quiet settings

noping noconfig homepage=about:blank

noping disables the machine ping for statistics as documented in privacy
noconfig disables the configuration service

Virtualbox settings

Using bridged networking (it's NAT by default) and filter in Wireshark on the eth.src address of your guest.

Packet sniffing under Windows

Besides NTP (for accurate time) and the usual router pings and such, you should see no automatic connections. This actually takes a lot of time and effort to turn off Firefox's automatic connections since they are so poorly documented and new ones seem to be constantly introduced.

Related project: https://github.com/pyllyukko/user.js

Be sure to check out the Webconverger packet sniffing videos for the upgrade scenario run through.