Before a browser connects to a named website, it normally needs to discover an address for that name. DNS supplies that lookup. DNS over HTTPS, often shortened to DoH, encrypts the exchange between the browser and the DNS resolver it uses.
That is a meaningful protection for a specific part of the process. It does not turn the entire internet connection into an anonymous tunnel.
Mozilla’s Firefox DNS over HTTPS guide explains the feature, its protection levels and situations where the browser may use different behaviour. Check the current settings on your device because defaults and available options can vary.
Separate the lookup from the visit
Think of a fictional visit to a recipe site as two questions. First: what address should the browser use for this name? Second: how does the browser communicate with the server at that address? DoH addresses the first exchange. HTTPS for the website addresses the protection of the web connection itself.
The chosen DNS resolver still receives the lookup it must answer. The destination website still receives your request, and logging into an account identifies you to that service. Cookies, account activity and information you submit do not disappear because the name lookup was encrypted.
There are also details outside the lookup. Network connections have destination addresses, timing and volume; the degree to which a domain name can be inferred or exposed depends on other technologies and the network. Do not assume that enabling one browser setting makes every browsing detail invisible.
Choose the setting for the actual device
On a personally managed computer, read the resolver’s privacy information and understand the browser’s fallback behaviour. On a school or workplace device, check the administrator’s requirements before changing name-resolution settings; internal services and managed controls may depend on them.
If a site stops opening after a change, record the browser version, setting and error message before troubleshooting. Do not disable unrelated security features at random. The useful question is whether the lookup, connection or website itself is failing—not whether “privacy mode” is simply on or off.