So I am trying to get started developing Office 365 Add-ins (previously Apps for Office), and I was wondering what browser or browser engine Office uses when it renders your app. I tried using JavaScript's navigator.appCodeName and navigator.appName, but due to the problem described here renders that method useless. What browser or engine do Office Add-ins use to render apps?
It depends on where Office is being used. If it's on Windows Desktop, Office Add-ins use an Internet Explorer to load the hosted webpage in Office. For iOS, it will rely on the native WebView control. If on Office Online, it will use a sandboxed iframe, in which ever browser you open Office Online with.
If you're trying to determine the browser Office is running in, I believe sniffing the user agent string will work for you.
来源：https://stackoverflow.com/questions/32039841/what-browser-browser-engine-do-office-add-ins-use