Configure Secure DNS on Firefox (DOH on Firefox)

Configuring DNS-over-HTTPS (DOH) in the Firefox browser will allow you to apply the custom filter settings for a sub-profile from your "Settings" page to the Firefox browser on a specific device.

1) Access the "Privacy & Security" section by going here in the Firefox browser (copy & paste into your address bar & hit ENTER): about:preferences#privacy

Alternatively, 

1. Click the menu button at the top right of the screen.
2. Click Settings.

2) Click "Privacy & Security" on the left

3) Scroll down the page until you see Enable DNS over HTTPS using:

4) Select the radio button by Increased Protection.  Under Choose provider: select Custom

5) Paste the "DNS over HTTPS" URL for the desired sub-profile.

6) There is no "Save" button - so just paste the URL and click outside of the field. If you like, you can visit another section of the browser settings and come back to see if your entry is still there.