Open Web App Manifest
An Open Web App is Mozilla's answer to the proprietary app stores. It is a website that has an acompanying manifest file which accomplishes such things as granting the "app" permission to access things on the user's device (such as contact lists) if it is properly installed, and giving it an icon which can be placed on a system desktop. When run, a web app behaves more like a native program than a website, even though it is actually being accessed on the web. These apps are supported by the Firefox browser on various platforms including Windows systems and Android mobile devices.
Manifest files are in JSON format and given a .webapp extension. The MIME type of application/x-web-app-manifest+json is used (enforced by the Firefox Marketplace, though not by the browser itself).