declarativeNetRequest
Also known as: dnr
The Manifest V3 API that lets extensions block or modify network requests using pre-declared rules.
declarativeNetRequest (DNR) is the engine the browser exposes to MV3 extensions for network filtering. Instead of running extension code on every request, the extension hands the browser a compiled rule set; the browser does the matching natively.
This is faster and more memory-efficient than the old webRequest model, and it means the extension doesn't need to see every request you make. The trade-off is that highly dynamic decisions (look up a domain in a remote API before deciding) are no longer possible.