The issue at root is determining what "functionality that the browser handles" should be. Every less-used option and feature that a browser can offload to an e

The issue at root is determining what "functionality that the browser handles" should be. Every less-used option and feature that a browser can offload to an extension or plugin is less code everyone has to download, and less code the browser team has to maintain. Also, those extensions can live or die based on actual usage and demand - a more fair "market economy" than the central browser team making those kinds of decisions about what's important or not. The alternative is tremendous browser bloat - supporting every feature wanted by 1% of users can lead to hundreds of extra features, and thousands more configurations that have to be regression tested.