When Firefox is set as the default PDF viewer, it automatically opens PDF files in the built-in viewer. However, you can choose to use another application to view your downloaded PDF files. This article will guide you on how to open PDF files with a different viewer, set another viewer as the default, or configure Firefox to always ask which viewer to use.

Use a different PDF viewer for a specific PDF file

You can choose to use another application to view a specific PDF file, by following these steps.

1. Open the Downloads panel by clicking the download icon next to the address bar.
2. Right-clickHold down the control key while you click the PDF file you want to open in a different viewer.
3. Click the option to open with your system’s default PDF viewer.

• For example, select Open in Adobe Acrobat Reader DCOpen in Preview.

Choose another PDF viewer to use by default or set Firefox to always ask

Disable the built-in PDF viewer and use another viewer

You can also set a different third-party PDF viewer to handle PDF files instead of Firefox’s built-in PDF viewer. To switch from using the built-in PDF viewer to another viewer:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. In the General panel, scroll down to the Applications section.
3. Find Portable Document Format (PDF) in the list and click the entry to select it.
4. Click the arrow under the Action column for the above entry and select the PDF viewer you wish to use from the drop-down menu.

Set Firefox to ask you what to do with PDF files

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. The next time you click a link to download a PDF file, Firefox will show you a prompt asking what to do with the file. You can then choose to open it with Firefox's built-in PDF viewer, open it with a different PDF application, or you can choose to save the file.

For more information, see Manage file types and download actions in Firefox.

Troubleshoot problems with the PDF viewer

• With certain types of PDF files, the PDF Viewer may have problems displaying fonts, colors, or the entire document. 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.
• If you can't open any PDF files with the built-in PDF viewer, a Firefox extension could be the cause. You can disable all of your extensions to see if one of them was the problem. For details, see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems.

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