title: Firefox 84.0 is changing custom file extension from downloaded file
body: <p>My web application creates a zip file to download files related to a &quot;Task&quot; instance. This zip file can contain images, .pdf or .txt files, the filename created has the form &quot;{taskName}.taskBundle&quot;.</p>
  <p>To download the file, the web application use the following headers in the response (from Firefox Network monitor):</p>
  <pre><code>Content-Disposition: attachment; filename=&quot;task1.taskBundle&quot;
  Content-Type: application/zip;charset=UTF-8
  </code></pre>
  <p><strong>The problem:</strong></p>
  <p>Using Firefox 84.0 (Ubuntu and Windows versions), the browser is replacing the '.taskBundle' extension by '.zip', so the downloaded filename is &quot;task1.zip&quot; instead of &quot;task1.taskBundle&quot;.</p>
  <p>I tried to download the same file with Chrome (87.0) and another Firefox versions (83.0, 82.0, 80.0, 74.0) and the file name is correct: &quot;task1.taskBundle&quot;.</p>
  <p>Maybe should I add another header to the response to prevent Firefox change the file extension?</p>
  <p>I can change the Content-Type to 'application/octet-stream' but the checkbox &quot;Do this automatically for files like this from now on.&quot; is not displayed in the download dialog.</p>
  <p>Additional notes:
  My app is written using Grails 3.3.9 but I think it is not a Grails issue because the response headers are sent to the client as described before.</p>