For Tab 3, you have to reply on individual apps to cast for you. Screen mirroring through Chromecast is NOT support on it yet. You may check this guide: https://allaboutchromecast.com/chromecast-how-to-guide/how-to-use-android-app-to-stream-local-media-files-to-chromecast/
Chrome Extensions are for PCs only. They are not available in Chrome for Android.
