Department of Defense
High Performance Computing Modernization Program

 Prior to 0.8, Firefox did not support IPv6. Since then, IPv6 has been supported by default and is preferred over IPv4. Firefox also requests AAAA DNS records even when there is no IPv6 connectivity.

To be certain that the IPv6 protocol is being used to access a website, substitute an IPv6 literal address surrounded by square brackets in place of a domain name. For example.

http://ipv6.test-ipv6.com

becomes

http://[2001:470:1:18::119].

For additional information, refer to Request For Comments (RFC) 3986 “Uniform Resource Identifier (URI): Generic Syntax".

(Caution: This substitution can sometimes fail. Explanation of possible reasons for this are available. If you encounter problems, review the Broken User FAQ article found on that website for several possible explanations. For even more possible explanations, review this article on the ARIN IPv6 wiki.)

To disable IPv6 support in Firefox:
1. In the Location bar, enter about:config. Then press the Enter or Return key
2. If the "This might void your warranty!" warning page appears, click I'll be careful, I promise! and then continue to the about:config page
3. In the Search field, type network.dns.disableIPv6
4. network.dns.disableIPv6 should now appear in the list of preferences. Set its value to true
5. Close the preferences

To re-enable IPv6 support in Firefox after it has been disabled, repeat steps 1 through 3 above. Then:
4. Set the value of network.dns.disableIPv6 to false
5. Check the value of network.dns.ipv4OnlyDomains. If it contains any domain names, delete them.
6. Close the preferences

One of the extensions available for FireFox is IPvFoo. After you install IPvFoo, a large 4 or 6 numeral will appear near the menu button (FireFox menu button). Clicking on that numeral will cause the IP address(es) of the web page you are viewing to appear. FireFox has many other extensions specific to IPv6. To view them, open the Add-ons manager, enter "IP" or "IPv6" (without the quotes) in the "Find more extensions" box, then press the Return key.


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