Some optional params

[dabevlohn]

network.connectivity-service.DNSv4.domain | localhost
network.connectivity-service.DNSv6.domain | localhost
network.connectivity-service.IPv4.url | http://localhost
network.connectivity-service.IPv6.url | http://localhost
network.connectivity-service.enabled | false
network.connectivity-service.nat64-check | false

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network.connectivity-service.DNSv4.domain | localhost network.connectivity-service.DNSv6.domain | localhost network.connectivity-service.IPv4.url | http://localhost network.connectivity-service.IPv6.url | http://localhost network.connectivity-service.enabled | false network.connectivity-service.nat64-check | false

it's enough to disable network.connectivity-service.enabled

also i recommend:
network.captive-portal-service.enabled false
app.update.BITS.enabled false
browser.startup.homepage_override.mstone ignore
dom.push.enabled false

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also check https://github.com/shawnanastasio/firefox-privacy-restorer/blob/master/firefox-privacy-restorer.py

browser.newtabpage.activity-stream.feeds.section.topstories.options ""
browser.newtabpage.activity-stream.feeds.section.topstories false

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official doc: https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/internals/preferences.html
https://kb.mozillazine.org/About:config_entries