Is the file downloading instead of opening? This can be the case if your settings in Firefox tell Firefox to download it automatically. This is easy to check. If you go to the download button (it's an arrow) in the Firefox toolbar after trying to open the PDF, is the file listed there? If so, it was saved to the computer, not opened. To change this behaviour, go to the Firefox settings and scroll down to the '''Applications''' section. You will see the '''Portable Document Format (PDF)''' content type listed there. Change the action to '''Open in Firefox'''. Hope this helps.