Recommended Firefox about:config settings

about:config.txt

# Recommended Firefox about:config settings

# Privacy
# https://support.mozilla.org/en-US/kb/how-stop-firefox-making-automatic-connections
extensions.blocklist.enabled;false
browser.safebrowsing.downloads.remote.enabled;false
browser.safebrowsing.malware.enabled;false
browser.safebrowsing.passwords.enabled;false
browser.safebrowsing.phishing.enabled;false
network.prefetch-next;false
network.dns.disablePrefetch;true
network.http.speculative-parallel-limit;0
browser.startup.homepage_override.mstone;ignore
extensions.getAddons.cache.enabled;false
captivedetect.canonicalURL;http://myip.tf/success.txt
network.connectivity-service.DNSv4.domain;v4.myip.tf
network.connectivity-service.DNSv6.domain;v6.myip.tf
network.connectivity-service.IPv4.url;http://v4.myip.tf/success.txt
network.connectivity-service.IPv6.url;http://v6.myip.tf/success.txt

# More privacy
browser.ping-centre.telemetry;false
permissions.eventTelemetry.enabled;false
toolkit.telemetry.enabled;false

# Enable security features
security.OCSP.enabled;1
security.OCSP.require;true
security.identityblock.show_extended_validation;true
security.tls.hello_downgrade_check;true
network.http.prompt-temp-redirect;true
accessibility.blockautorefresh;true

# Disable user-hostile security features
security.cert_pinning.enforcement_level;0
network.stricttransportsecurity.preloadlist;false

# Disable useless protocols and features
security.tls.enable_0rtt_data;false
security.tls.version.fallback-limit;3
security.tls.version.max;3
security.tls.version.min;3
network.http.spdy.enabled;false
network.trr.mode;5
browser.send_pings;false
beacon.enabled;false
clipboard.autocopy;false
dom.event.clipboardevents.enabled;false
browser.cache.memory.enable;false
extensions.pocket.enabled;false

## Old list, has duplicates

accessibility.blockautorefresh;true
accessibility.typeaheadfind;true
accessibility.typeaheadfind.flashBar;0
browser.contentblocking.category;custom
browser.safebrowsing.malware.enabled;false
browser.search.suggest.enabled;false
browser.search.update;false
browser.zoom.siteSpecific;false
datareporting.healthreport.uploadEnabled;false
devtools.onboarding.telemetry.logged;false

# Disable Pocket
extensions.pocket.enabled;false

# Most common accept-languages
intl.accept_languages;en-US, en

# Disable Digital Restrictions Management
media.eme.enabled;false

# Disable HTTP/2
network.http.spdy.enabled;false

# Various prefetch stuff
network.dns.disablePrefetch;true
network.predictor.enabled;false
network.prefetch-next;false

# Only allow TLS 1.2
security.tls.enable_0rtt_data;false
security.tls.version.fallback-limit;3
security.tls.version.max;3
security.tls.version.min;3

# Do not send pings
browser.send_pings;false

# Dsable Safe Browsing
browser.safebrowsing.blockedURIs.enabled;false
browser.safebrowsing.downloads.enabled;false
browser.safebrowsing.downloads.remote.url;
browser.safebrowsing.downloads.remote.enabled;false
browser.safebrowsing.malware.enabled;false

Sounds like most of browser.safebrowsing.* are actually fairly safe... EXCEPT browser.safebrowsing.*.remote
If your goal is entirely "stop-firefox-making-automatic-connections" then fair enough.
If your goal is privacy / security, browser.safebrowsing is "only" downloading big lists of unsafe URLs, not reporting back any/all URLs you're visiting (except the "remote" ones - disable those)