Alongside of the announcement of Windows 10 Insider Preview build 18358 in the Fast ring, Microsoft announced that it's releasing a Windows Defender Application Guard extension for Chrome and Firefox. It's exclusive to Insiders for now, but it will be available for everyone soon.
The way it works is the same way it does in Edge, but checking the URL you navigate to against a list of trusted websites. If it's found that you're navigating to an untrusted site, it will open in a sandboxed Microsoft Edge browser. From there, you can navigate to any website, whether it's trusted or not, as it won't be able to harm your system.
After installing the extension, you'll see a Windows Defender Application Guard landing page when you open Chrome or Firefox. You'll see the Windows Defender icon in the browser, and you can start an Application Guard session by clicking on it and entering a URL.
While the extension is only live for Insiders right now, you'll be able to use it on Windows 10 version 1803 or higher when it's publicly available, though you'll need Windows 10 Pro or Enterprise. You can download them at the following links: