browser-extension

Manifest V3 browser extensions require a manifest.json file declaring permissions, host_permissions, and a service worker for background logic. Set manifest_version to 3, define your extension's capabilities, create a service worker file, and package the extension directory to load it unpacked in Chrome, Firefox, or Edge for testing and distribution.

Content scripts inject into web pages to interact with page content and communicate with your extension via isolated world messaging. Service workers run persistently in the background to handle events, manage permissions, and coordinate extension logic without direct page access, replacing the older background page model.

Manifest V3 extensions work across Chrome, Firefox, and Edge with a shared codebase, though cross-browser compatibility requires testing platform-specific behaviors. Use the core MV3 structure and manifest.json configuration, then test and adjust for minor differences in each browser's implementation.

Define popup and options_page paths in manifest.json pointing to HTML files. Create corresponding UI components with HTML, CSS, and JavaScript that communicate with your service worker using chrome.runtime messaging. Package these files with your manifest and other extension assets for a complete extension interface.

MV3 extensions require two permission types in manifest.json: permissions for APIs your extension uses (storage, tabs, webRequest) and host_permissions for specific URLs or patterns the extension accesses. Declare only necessary permissions to comply with store requirements and security best practices.

Load your extension unpacked by enabling Developer Mode in the browser's extension management page, then selecting your project directory. The browser loads all files from that directory, allowing you to test changes by reloading the extension after edits to manifest.json, service workers, or UI components.