The only web page I have opened today with this machine is in deed the page of my router (http://192.168.100.1:80) as confirmed by 'visited pages'. Could the remote web addresses which we saw in the netstats belong to anything queried by some Firefox
Note that Firefox makes a good number of network requests whenever it starts, unless you have modified it not to do so. These include: Heartbeat https://wiki.mozilla.org/Advocacy/heartbeat Google's safe browsing, malware, and phishing protection https://www.privacytools.io/#about_config And various Akamai servers to check for add-on updates. That's all that I can remember off the top of my head, but do not expect Firefox to not make network requests simply because you have not navigated to any websites.