I'm not sure , but i guess `skip-AAAA-when-not-supported` may not be implemented yet after searching `https://searchfox.org/mozilla-central/search?q=skip-AAAA-when-not-supported&path=&case=false®exp=false` Have you tried `network.dns.disableIPv6` option ?
Bug 1852899 Comment 1 Edit History
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I'm not sure , but i guess `skip-AAAA-when-not-supported` may not be implemented yet after searching https://searchfox.org/mozilla-central/search?q=skip-AAAA-when-not-supported&path=&case=false®exp=false Have you tried `network.dns.disableIPv6` option ?