If you don’t know Mozilla working on Open Web Apps project which is much like Chrome Web Store but lets you install apps on any modern browser supports basic HTML features (other browser should support this platform) from Mozilla store or directory. Mozilla Web App store will be integrated into Firefox once its launched and lets you access installed apps from button on the toolbar/add-on bar. Installed apps will be opened in app tabs (occupies less space on tab bar) and recognized as web apps across the sessions.
Mozilla currently offering experimental Open Web App for Firefox extension for interested users to test some sample web apps from their app directory. These web apps can be build by developers using HTML 5, JavaScript and CSS web technologies.
You can view and manage the installed apps from dashboard as well as from about:apps page. These installed web apps will be synchronized across all devices with integration with Firefox Sync. These apps can be available as free and paid.
One feature of Open Web Apps feature is App Discovery, browser automatically discovers the associated app for the website when you visit and prompts you to install it, for example if you visit Twitter website, Firefox discovers the app for twitter website and offers app to install without the need to search for it. Similarly if you visit a web site for which app already installed that app takes over and displays the page in it. Another feature is Web Activities where one site able to connect to other site mediated by the browser. Check the below video to understand that.