How to disable PDF viewing in Firefox
You may already encountered websites that provide link to a PDF file, usually if you installed Adobe Reader you will be able to automatically view the PDF files right inside your browser.
The trouble with this method is, your browser may freeze or crash while waiting for the PDF files to download to your computer. Furthermore, some people view this feature as a drawback because Web browser should not takeover PDF reader job.
The Solution

Fear not because somebody has published a quick fix that disable firefox capability to display PDF files on the fly.
Please proceed to Disabling PDF Display in Firefox













Actually, there is an alternative… you can install an extension called PDF Download. Once enabled, instead of opening the PDF file directly, Firefox will ask if you want to download the file, open the file or view as HTML.
It is still not perfect yet… sometimes it still does open the PDF file directly, but it’s usually a link from an external programme… Of course your recommended method is the best if your choice is always to download the file.