Firefox About Config

Firefox can support IPv6 without any problem. Unless you’ve been disabled the Firefox’s IPv6 resolve before this.
From the picture above, it is pretty straight forward on how to re-enable back IPv6 DNS resolve for Firefox.

At the address bar, just type in “about:config”, then you will be greeted with the “This might void your warranty” page.
Just click on the “I’ll be careful, I promise!” and proceed. Since when Firefox got warranty anyway? It is a free software after all.
Now, the advance configuration page will appear. Just type in “ipv6” in the “Filter” area, then you can see the “network.dns.disableIPv6”. Just click it and press enter, it will toggle back to “false”.
Make sure the “Value” is false, because we want to prevent the disability of IPv6.

Ok, now you are free to close that page and continue to browse any IPv6 capable websites.