User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:70.0) Gecko/20100101 Firefox/70.0

Steps to reproduce:

Attempted to open a PDF from a URL

Actual results:

Browser attempted to load a file path in temporary storage for the PDF and continued to open new tabs in an endless loop.

Since the browser kept taking focus, it was actually really difficult to kill firefox. Tested with multiple PDFs from different websites.

Expected results:

Prompt user to download PDF or view in browser.

Reliably reproducible for me when opening any PDFs specifically from a file, regardless of location. Tested with a local html file with no issues.

Enter about:preferences into the address bar and set the action for PDF to Preview in Firefox or anything other than opening with Firefox.