J. P. Gilliver (John) wrote:

I did it, and (I'm running XP) it said

Successfully flushed the DNS Resolver Cache.

I then did ipconfig /displaydns | find "Time To Live" again, and it
looked to still have the same number of lines; doing it without the pipe
to "find" (piping to "more" instead) looks the same, too.

Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es
\DNSCache\Parameters

Data: MaxCacheEntryTtlLimit (DWORD)
Default value is 86,400 seconds (1 day)
How long a positive DNS query remains locally cached.

Data: NegativeCacheTime value (DWORD)
Default value is 300 seconds.
How long a negative DNS query (failure) remains cached.

Defaults get used if the registry entry is not defined. Setting
MaxCacheEntryTtlLimit to 1 effectively disables the local DNS cache (TTL
is only 1 second). This is what Microsoft recommends. Don't know what
happens if you set it to 0 (sometimes endpoints in a range have special
meaning so maybe 0 means indefinite caching time). You could also
disable the "DNS Client" service (stop and set to Disable startup mode)
and then also flush the current cache contents. Of course, that means
if a web page has hundreds of hostnames all of which need to be resolved
(they are absolutely pathed to the same or different domain versus
relatively path to the same host) then you will be making a lot more DNS
requests outside your host to whatever DNS server you use.

Firefox has its own internal DNS cache. To disable it, set
network.dnsCacheExpiration to 0 (zero) - which means you would use
Windows local DNS cache unless that was also disabled which means you
would also issue DNS requests to an outside DNS server for every
non-relatively pathed resource in a web page (which could be scripts,
CSS, and other non-ad/tracking resources).

Note: Just because an old setting is still listed in about:config does
not mean Firefox still honors it. I've read contradicting articles
dated July 2016 claiming that a "new version" (not mentioned) has
Firefox using the local DNS cache in the OS. In FF 47.0.1, the
about:cache page is still defined (and mine shows non-zero values), so
maybe some near-future version is going to drop the internal DNS cache.