I recently updated my Mozilla Firefox. Firefox now includes a built-in PDF viewer that allows me to see PDF files found on the web without a plugin. The built-in PDF viewer is enabled by default. However, I found that this pdf viewer is not working properly with various web-sites, and it works slowly. How do disable the built-in PDF viewer so that I can use the Adobe PDF viewer or other PDF viewer that is shipped with my operating systems?

Firefox can display PDF files using the any one of the following method:

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[a] Built-in PDF Viewer.

[b] PDF reader plugin.

[c] Download and use local pdf reader and more.

Option #1: Set pdf Firefox options

MS-Windows user at the top of the Firefox window, click on the Firefox button and then select Options. Select Applications tab.

A note about Linux users

From the menu bar > Edit > Preferences > Select Applications tab.
Sample outputs:

Define the default action for the PDF file:

To change how Firefox handles a pdf file type in the list (type pdf in box), click on its name to select it. Open the drop-down menu to select the download action you want Firefox to use:

1. Choose an application: To choose a local or web application to handle a type, select the application from the drop-down menu. If you want a local application that is not in the menu to handle the type, select Use other… from the drop-down menu and point Firefox to its location.
2. Choose a feature or plugin: If you want a feature or a plugin in Firefox to handle the type, and one is available, select it from the drop-down menu.
3. Save on your computer: Some file types can be saved to your computer. Select Save File from the menu for one of these file types to have Firefox save that type of file to the location specified in the Downloads settings.

Finally, click on the Close button.

Check out related media

This tutorial is also available in a quick video format:

Video 01: Firefox: Disable The New built-in PDF-viewer Under Linux or Unix Oses

Option #2: Set pdfjs.disabled option

Type the following in Location Bar (address bar)
about:config
Sample outputs:

Click the button labeled “I’ll be careful, I promise!“. Type the following in Search bar:
pdfjs.disabled
Click on its name to select it > Right click on pdfjs.disabled entry > Select Toggle (set it to TRUE).

How do I test new settings?

=> Visit this url and download pdf file.