This guide explains how to enable DNS over HTTPS (DoH) in the Firefox browser and route requests through your personal ADnull DNS.
Step 1. Open Firefox Settings
Click the three horizontal lines ☰ in the top right corner → Settings.
Step 2. Go to Privacy & Security
Select Privacy & Security from the left menu.
Step 3. Find the DNS over HTTPS section
Scroll down to the DNS over HTTPS section → enable it → select the protection level Max Protection or Increased Protection → in the Provider field choose Custom.
Step 4. Enter the DoH address
Paste the address into the Custom field:
https://YOUR-SUBDOMAIN.dns.adnull.com/dns-query
Replace YOUR-SUBDOMAIN with your personal subdomain — it is shown in the Settings section of your ADnull account.
Settings are saved automatically.
Done!
Firefox now uses ADnull DNS. Ads and trackers are blocked at the DNS level in your browser.
FAQ
Where do I find my subdomain?
Go to the Settings section in your ADnull account — the subdomain is shown in the "DNS Domain" card.
DoH was not applied after configuration
Restart Firefox. Also make sure that no proxy or VPN in your network settings is intercepting DNS requests.
What is the difference between Max Protection and Increased Protection?
Max Protection — all DNS requests go through DoH; if DoH is unavailable, Firefox will block the connection.
Increased Protection — DoH is used when possible, but falls back to the system DNS if needed.