WebExtensions API

A cross-browser system for building browser extensions using standard HTML, CSS, and JavaScript APIs.

The WebExtensions API provides a unified framework for developers to build powerful browser enhancements compatible with Chrome, Firefox, Safari, and Edge. By utilizing the manifest.json file and standardized JavaScript APIs (such as tabs, storage, and runtime), developers can write a single codebase that reaches billions of users. This system replaced legacy architectures like XUL and XPCOM, ensuring better security through sandboxing and improved performance via non-blocking asynchronous calls. Whether you are building an ad blocker, a password manager, or a productivity tool, this API offers the essential hooks into browser UI and network traffic needed for modern web customization.

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions