title: Fix "This file is not commonly downloaded" warning - Firefox only
body: <p>I run a website (<a href="https://www.pixelscrapper.com" rel="noreferrer">www.pixelscrapper.com</a>) that serves file downloads of images, and zipped collections of images (which are zip files containing multiple imags, psds, vectors, etc.) <strong>These files are hosted on Amazon S3, and served via download urls generated by aws sdk for php (v1)</strong>.</p>
  
  <p>Just recently, users trying to download our zip files using Firefox have started getting "This file is not commonly downloaded" warnings (<em>after the download finishes</em>), which forces them to override the warning before accessing the file via the Firefox download manager. Naturally, this kind of warning causes concern for our users. </p>
  
  <p><a href="https://i.stack.imgur.com/Q1NYC.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Q1NYC.png" alt="not commonly downloaded warning"></a></p>
  
  <p><strong>This warning shows up IN FIREFOX ONLY</strong>--Chrome, Edge, and Internet Explorer show no warnings when downloading and opening our zip files. The warning also only seems to show up for (surprise, surprise) files that have been more recently added to the site, and have relatively few total downloads--but many of our files never receive large numbers of downloads, so this warning has the potential to plague many of our files indefinitely.</p>
  
  <p><strong>My question is: is there anything I can do to prevent this warning?</strong> By adjusting headers, signing files in some way, etc.? (From what I understand, Chrome and Edge also have "uncommon file" warning, but they don't seem to be concerned with our files--why is this warning only firing in Firefox?) I've searched around on Stack Overflow and elsewhere, but most of the questions I've seen about "uncommon download" warnings are targeted at Chrome or Internet Explorer, and I can't seem to find any Firefox-specific information about this warning.</p>
  
  <p><strong>Here's a sample file download url (generated by aws sdk) that is causing warnings:</strong> </p>
  
  <pre><code>https://pixelscrapper-user-content.s3.amazonaws.com/template-attachment/user-2/node-13574/paper-037-template-polka-dots.zip?response-content-disposition=attachment%3B%20filename%3D%22ps_marisa-lerin_13574_paper-037-template-polka-dots_cu.zip%22&amp;AWSAccessKeyId=AKIAIWM7MZMHRPA6FHEA&amp;Expires=1495386939&amp;Signature=HDmwRFPX81CIVrQgu1BkEyR9iRQ%3D
  </code></pre>
  
  <p>Here's an inspection of headers in Firefox:</p>
  
  <p><a href="https://i.stack.imgur.com/taXog.png" rel="noreferrer"><img src="https://i.stack.imgur.com/taXog.png" alt="file headers"></a></p>
  
  <hr>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>The issue here is not the nasty-looking url generated by the aws sdk: I checked downloading the same zip file (containing one jpg, one psd) from the following "clean" url, and it still gives the warning: <a href="http://pixelscrapper-misc-files.s3.amazonaws.com/ps_marisa-lerin_13574_paper-037-template-polka-dots_cu.zip" rel="noreferrer">http://pixelscrapper-misc-files.s3.amazonaws.com/ps_marisa-lerin_13574_paper-037-template-polka-dots_cu.zip</a></p>