If some PDF files don't render well or are blank, click the download button on the right side of the document header to open it with the default PDF viewer application on your computer. With certain types of PDF files, the PDF Viewer may have problems displaying fonts, colors, or the whole document.Troubleshoot problems with the PDF viewer The current view button to open the current view in another tab or window.
If you want Firefox to always ask you what to do with PDF files, follow the above steps to change the action for the Portable Document Format (PDF) entry, except select Always ask from the drop-down menu. Set Firefox to ask you what to do with PDF files Note: When Open in Firefox is the selected action, the built-in PDF viewer is used. Click on the arrow under the Action column for the above entry and select the PDF viewer you wish to use from the drop-down menu.Find Portable Document Format (PDF) in the list and click on the entry to select it.In the General panel, go down to the Applications section.Click the menu button and select Settings.
Click the menu button and select Options Preferences. In the Menu bar at the top of the screen, click Firefox and select Preferences. To switch from using the built-in PDF viewer to another viewer:
You can also set a different third-party PDF viewer to handle PDF files, instead of Firefox’s built-in PDF viewer.