Affected versions

• Firefox 72.0a1 (BuildId:20191121214422)
• Firefox 71.0b11 (BuildId:20191118154140)

Affected platforms

• Windows 10 64bit.

Preconditions

• Launch Firefox and set the network.trr.mode pref to 2.
• Enable the DNS Suffix search list option and add a random domain inside the “DNS Suffixes” field from via gpedit.

Steps to reproduce

1. Access the about:networking#dns page.
2. Access the domain entered via gpedit.

Expected result

• For Step 1: The DNS suffix entered via gpedit is displayed inside the about:networking#dns page under the DNS suffix list.
• For step 2: The domain is displayed as TRR false inside the about:networking#dns page.

Actual result

• For Step 1: The DNS suffix entered via gpedit is not displayed inside the about:networking#dns page under the DNS suffix list.
• For step 2: The domain has been handled via TRR.

Regression Range

• I don’t think that this is a regression.

Notes

• Please note that you may have to disconnect/reconnect to your network after applying the changes inside gpedit. Also a refresh to the about:networking#dns page may be needed.
• On Nightly, due to patch for Bug 1597683, setting the DNS suffix list via “Advanced TCP/IP Settings” is successfully parsed by Fx. The changes performed in “Advanced TCP/IP Settings” reflect inside Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
• Setting the DNS suffix search list via gpedit reflects inside Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient and overrides the settings applied inside the “Advanced TCP/IP Settings” UI panel (see the attached screenshot).

We probably want to deal with this case as well. Targetting 73.

Bugbug thinks this bug is a regression, but please revert this change in case of error.

Bug 1597683, added support for setting the DNS suffix list via "Advanced TCP/IP Settings". The changes performed in "Advanced TCP/IP Settings" reflect inside the Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters registry key.

However, when setting the Local Group Policy for DNS Suffixes via gpedit, the registry key that gets modified is Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient
Note: the setting in gpedit can be found at Computer Configuration > Administrative Templates > Network > DNS Client > DNS suffix search list

This patch first checks for the Local Group Policy registry key, and if not found it checks the one that gets set by the Advanced TCP/IP Settings window.

https://hg.mozilla.org/mozilla-central/rev/0559b672dbd9

I verified this issue using Fx 73.0b12 and Fx 73.0 on Windows 10 x64.