Latest Amazon Kindle Fire HDX 8.9" 4G user agents:

User Agent	Browser	Platform
Mozilla/5.0 (Linux; U; Android 4.4.3; en-us; KFAPWA Build/KTU84M) AppleWebKit/537.36 (KHTML, like Gecko) Silk/3.68 like Chrome/39.0.2171.93 Safari/537.36	Mobile Silk 3	Fire OS 4
Mozilla/5.0 (Linux; Android 4.4.3; KFAPWA) AppleWebKit/537.36 (KHTML, like Gecko) Silk/81.2.16 like Chrome/81.0.4044.138 Safari/537.36	Mobile Silk 81	Fire OS 4