The full installer is actually responsible for installing the browser; it’s what the stub launches in order to do the “real” installing work, but it’s also available separately. It uses a traditional “wizard” interface design, as is (somewhat) natively supported by NSIS. It can also be configured to launch in a silent mode, suitable for scripting or managed deployments.
The full installer’s main script is installer.nsi, but most of the heavy lifting is done by the shared functions in common.nsh.
If it was not launched by the Stub Installer, an Install Ping is sent when the installer exits.
The installer writes
installation_telemetry.json to the install location, this is read by Firefox in order to send a telemetry event, see the event definition in Events.yaml (category
installation, event name
first_seen) for a description of the properties. There is also an
install_timestamp property, which is saved in the profile to determine whether there has been a new installation; this is not sent as part of the ping.