According to MSDN Blogs, This appears to be a Web Essentials 2013 extension of Browser Link capability. Visual Studio provides extensibility for Browser Link which Hanselman was sharing.
When viewing the site, you can use CTRL + ALT + D to enable Design Mode which updates the Visual Studio source. Web Browser Design Mode for Browser Link is browser independent. To enable it for non-Debug mode, you need to add the following appSettings
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<add key="vs:enableBrowserLink" value="true" />