1981521 - Firefox on Android prefers IPv4 over IPv6

Status: UNCONFIRMED

(Core :: Networking, enhancement, P3)

Description

[doug.hs]

Attachment: Captura de tela de 2025-08-06 12-59-48.png

Steps to reproduce:

1. Connect phone to a computer and use USB Debugging to inspect Firefox on Android
2. Go to a domain that you know resolves to IPv4 and IPv6
3. Check the resolved IP in the Network tab

Actual results:

The website prefers the private IPv4 instead of the IPv6 ULA.

Expected results:

Prefer IPv6

Comment 1

[doug.hs]

Attachment: DNS lookup for the tested domain

In this screenshot you can see the output of nslookup showing that it resolves to 192.168.1.106 and fd17:3cb2:d446:0:dea6:32ff:fe9c:c7ca.

Comment 2

[doug.hs]

Attachment: nslookup on Android

The previous screenshot was on the computer. This one is from the Android phone.

Notice that IPv4 is on top. (not sure the order means anything)

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Firefox for Android::Browser Engine' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 4

[Makoto Kato [:m_kato]]

Moving to Core: Network

Comment 5

[Valentin Gosu [:valentin] (he/him)]

Could you go to about:config and set network.dns.preferIPv6 to true?

Comment 6

[doug.hs]

I cannot find about:config on Firefox for Android. That page doesn't seem to exist there.

Comment 7

[Valentin Gosu [:valentin] (he/him)]

(In reply to doug.hs from comment #6)

I cannot find about:config on Firefox for Android. That page doesn't seem to exist there.

That page is only available on Firefox for Android in Beta and Nightly.
We'll probably flip the pref by default, but to avoid regressions we'll wait for bug 1953459 to land first.