Anyone else was under a naive impression that the preview would go through the Mozilla servers? something like DuckDuckGo has(had? haven't used it for a while)
Just to be explicit: it doesn't go through any server, all processing happens on your device.
Edit: ah, just saw the clarification. So the content is not sent anywhere to create the summary, but you do visit the original site, just like you would have if you had done a regular click.