Once the native platform (iOS, Android or Windows) initializes the web framework, you can access MobileFirst functionality from the WebView with JavaScript.
You can use Cordova plug-ins or HTML 5 to create JavaScript API to call user-interface controls that are common to most environments, such as modal pop-up windows, loading screens, or tab bars.
From MobileFirst 8.0 you can integrate Crosswalk WebView with your Cordova MobileFirst app. See Crosswalk WebView (Android).
Whether you choose to integrate Crosswalk or use the default Cordova WebView a wide range of MobileFirst functionality is available using JavaScript. See Some initial WebView code for connecting to the server.