title: How do websites know they're not the default home page or search provider?
body: <p>As far as I'm aware, there is no public API exposure of a browser's default homepage/search provider. So how does Google know to display this? It only comes around when Google's not the default homepage / default search provider on my browser.</p>
  
  <p><a href="https://i.stack.imgur.com/VkJ3d.png" rel="noreferrer"><img src="https://i.stack.imgur.com/VkJ3dm.png" alt="Google on-page popup: &#39;Get to Google faster. Switch your default search engine to Google.&#39;"></a>
  <a href="https://i.stack.imgur.com/NGAZH.png" rel="noreferrer"><img src="https://i.stack.imgur.com/NGAZHm.png" alt="Googe on-page popup: &#39;Come here often? Make Google your homepage.&#39;"></a></p>
  
  <p>I can only assume they're inferring from numerous variables, such as the referrer. I wasn't able to successfully dig down into Google's compiled JavaScript. I'm not even sure if it's detected client-side or server-side. </p>
  
  <p>I'm on Firefox 44, but I've seen these banners on Chrome, too. </p>