Mozilla has begun to enable DNS-over-HTTPS (DoH) by default for users in the USA to provide encrypted DNS resolution and increased privacy. DoH is a new standard that allows web browsers to perform DNS resolution over encrypted HTTPS connections rather than through plain text DNS lookups. Mozilla has stated that this will be a gradual rollout of the DoH feature, which means that it will be done slowly over the next few weeks to make sure there are no issues with the implementation as more people begin to use it.
Source: https://www.bleepingcomputer.com/news/software/mozilla-enables-dns-over-https-by-default-for-all-usa-users/