To enable DoH, click the three horizontal bars in the top-right corner of Firefox and then select the “Options” button. (Click “Preferences” if you’re on macOS.)
Locate the “Network Settings” heading and then click the “Settings” button.
Scroll down to “Enable DNS Over HTTPS” and check or uncheck the corresponding box to turn the setting on or off.
When you enable DNS over HTTPS this way, Firefox will use the Cloudflare DNS by default. You can change your DNS by clicking the “Use Provider” drop-down menu and clicking either “NextDNS” to use Mozilla’s chosen alternative, or “Custom” to input your DNS server address of choice manually. However, DNS over HTTPS will only work if your selected DNS server has enabled support for it. You can’t just use any old DNS server.
Even if you don’t enable DoH manually, Firefox will automatically enable it for you over the next few weeks—assuming you’re in the U.S. We expect Mozilla will automatically enable DoH for people in other countries in the future, too.