How can I enable or disable the built-in PDF viewer in Mozilla Firefox?

@naomi_cronin 

To enable or disable the built-in PDF viewer in Mozilla Firefox, follow these steps:

1. Open Firefox and type "about:config" in the address bar. Press Enter.
2. You will see a warning message. Click on "Accept the Risk and Continue" to proceed.
3. In the search bar at the top, type "pdfjs.disabled".
4. You will see a preference named "pdfjs.disabled" listed below. Double-click on it to change its value.
5. To disable the built-in PDF viewer, set the value to "true".
6. To enable the built-in PDF viewer, set the value to "false".
7. Close the about:config tab.

After making this change, Firefox will either use its built-in PDF viewer or download the PDF files, depending on your preference.