How to Disable in-built PDF Viewer in Mozilla Firefox

Starting with the version 19 of Mozilla Firefox, the popular browser has started to show the PDF files right inside your web browser using an in-built PDF viewer without using any third party plugins from Adobe or any other company. This is a great feature as now you do not need to download the PDF files first and then open them using a PDF reader application. Google Chrome had already provided this feature many versions ago. The in-built PDF viewer in Firefox has an option to download the file too. But this in-built PDF reader cannot handle all kinds of PDF files as some of the PDF files have advanced features in them. If you want to disable the in-built PDF viewer in Firefox, then you can follow these simple steps :

  1. Open Mozilla Firefox browser. In the location bar type about:config and press Enter.
  2. Firefox will show a warning. Click on the button labeled I’ll be careful I promise! to proceed.

    Disable in-built PDF Viewer in Firefox

  3. In the Filter field type pdfjs. You would see a preference named pdfjs.disabled as shown.

    Disable in-built PDF Viewer in Firefox

  4. Double click on pdfjs.disabled to change its value to true.
  5. After changing the value, restart the browser for the changes to take effect.

After disabling the in-built PDF viewer in Mozilla Firefox, when you click on a PDF file link, it would open the usual file download window or start downloading it to your pre-selected download folder (as per your configuration settings of Firefox). Once the download is complete, you can open the downloaded PDF file in your default PDF reader application like Adobe PDF Reader or Foxit PDF Reader etc.