What are the main differences between the Manifest V2 and Manifest V3 specifications for extensions?

The transition of the extension ecosystem to the Manifest V3 specification has been one of the largest architectural changes in modern browsers in recent years. Developers state that the main goal of this update is to increase the level of security, improve user data privacy metrics, and optimize overall system resource consumption. The old standard is being gradually phased out and completely replaced by the new one.

One of the key technical innovations is the replacement of background pages, which used to run constantly, with service workers. Service workers are launched by the operating system only when they are actually needed and are automatically unloaded from memory during periods of inactivity, which significantly reduces the load on the computer's CPU and RAM. In addition, the approach to handling network requests has changed: instead of the old blocking API, a declarative interface is now used, which processes rules on the browser side without sending every request to the extension's code.

Also in Manifest V3, the rules for loading and executing external remote code have been tightened. Developers can no longer use scripts loaded from third-party servers while the extension is running; all executable code must be packaged directly into the distribution and undergo preliminary moderation in the add-ons catalog. This innovation is critically important for protecting users against potential supply chain attacks and unauthorized changes to the logic of installed programs.