Manifest V3 is the latest version of the extensions platform. We have made a number of changes to the available APIs and added a number of new features.
Extensions in Manifest V2 had a long-lived background page that took up resources, even when an extension wasn't running. In Manifest V3, we have moved the background context to service workers, which run only when needed.
We are deprecating the blocking version of the webRequest API. This required extensions to proxy all network traffic to provide filtering capabilities, which came at a performance and privacy cost. The new declarativeNetRequest API provides a safer alternative for many use cases.