The extension model is the browser framework that lets add-ons extend functionality through approved APIs, permissions, and UI integration. It makes browsers more useful by allowing tools such as password managers, ad blockers, and enterprise workflow helpers to inspect pages, modify content, and respond to events. That flexibility also expands the trusted computing surface: every installed extension is another piece of code that may handle sensitive page data, credentials, and sessions.
In cyber security, the extension model matters because attackers often target it. A malicious or compromised extension can steal browser data, inject content, redirect traffic, or weaken security controls. Defenders reduce risk by limiting installation to trusted sources, reviewing requested permissions, enforcing allowlists, and removing unused add-ons. In enterprise environments, extension policies are a common control for keeping browsers functional without giving away unnecessary trust.