title: Detect if Safari Extension is Installed
body: <p>Is there a way through JavaScript to detect if a Safari Extension is already installed? <a href="https://extensions.apple.com" rel="nofollow">https://extensions.apple.com</a> has some way of doing it because they update the install link to "installed" if the extension is already installed. However, I can't figure out how they do it. I've traced it back to an object of type 'SafariExtensionGalleryController" but that's as far as I get.</p>
  
  <p>Did Apple put special hooks into the extension system just for their stuff??</p>
  
  <p>Lost...</p>
  
  <p>Thx, Joel </p>