A CRX file is a package file format used by Google Chrome and Chromium-based browsers (like Brave, Edge, and Opera) to distribute extensions, themes, and packaged apps. It's essentially a ZIP archive that contains all the files necessary for the extension to function, including HTML, CSS, JavaScript, images, and a manifest file (manifest.json) that describes the extension's metadata, permissions, and entry points. When you install an extension from the Chrome Web Store or load an unpacked extension, the browser unpacks the CRX file and installs the extension into the browser's profile directory. The CRX format ensures the integrity and security of extensions by including a digital signature that verifies the extension's authenticity and prevents tampering. This helps protect users from malicious extensions that could compromise their privacy or security. CRX files are not meant to be opened directly by users; instead, they are installed through the browser's extension management interface.