When visiting a web page, your browser makes a request (normally to your internet service provider) to turn the web address you’ve typed into an IP address. This request is made over an insecure, un-encrypted connection even if the site itself is secure and if you’re using In-Private or Incognito browsing.
What this means is that your internet service provider can see what web sites you are visiting. Even if they can’t see the content due to encryption.
With a recent release, the Firefox browser aims to help provide users with more privacy by provide this name resolution service over an encrypted channel. This prevents internet providers from knowing anything about the sites which you are visiting.
To find out how to enable this feature within Firefox, visit their page on enabling DNS over HTTPS here:
https://support.mozilla.org/en-US/kb/firefox-dns-over-https
