Environment: Windows 10 Pro x64, Google Pixel 3 a (Android 9)
Build: Fenix Nightly/Firefox Preview Nightly 191126 (Build #13300628) with Gecko View 72.0a1-20191119043902

Steps to reproduce:

1. Create a hot spot connection from laptop to mobile.
2. Go to Registry Editor path "Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters"
3. Change the DNS suffix from the default one "mshome.net" in ICS Domain register to "gsp.ro".
4. Connect the mobile device to the newly created hotspot network.
5. Open Fenix app.
6. Insert in URL bar "about:config" and set in the field for the "network.trr.mode" value "2".
7. Make a search after the domain from step 3.
8. Insert in URL bar "about:networking" and tap on the "DNS" section.
9. Inspect the "DNS Suffix:" field and the information from "TRR" column.

Expected Result:
The "DNS Suffix" displays the one from the registry key. In our case "gsp.ro"
The "TRR" column displays value "false" because they are not resolved through TRR option.

Actual Result:
The "DNS Suffix" displays the one from the registry key. In our case "gsp.ro"
The "TRR" column displays value "true", it should be resolved through native DNS and not recognized as resolved though TRR.

Note: In order to check that the dns suffix is applied waited a couple of minutes - approximately 5 minutes.

Hi, verified the issue as fixed on Firefox Preview Beta 3.2.0-beta.3 GV: 73.0-20200123180644 with Google Pixel 3a XL (Android 9). Now the request is made with value false on TRR column. The request was solve through DNS. Will leave the ticket as it is until reaches Firefox Preview RC version.

Thank you for checking, Diana!

Seems like this is fixed now.