You should never select Firefox as the application to handle a file via the "open with" dialog. In this case you should instead select "Preview in Firefox" for Portable Document Format (PDF) in "Options/Preferences -> Applications".

• https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file

You get tabs opening endlessly if you select Firefox as the application to handle a file when you get an "Open with" dialog.

• https://support.mozilla.org/en-US/kb/Firefox+keeps+opening+many+tabs+or+windows

I have PDF set to "Preview in Firefox". With some PDFs (not all), a separate windows opens and infinite tabs open. I have to quit Firefox to get this to stop. This is really frustrating. This has happened over multiple Firefox versions over the last couple of years. I'm currently on 69.0b4 64-bit on macOS 10.14.6. Chrome handles this flawlessly.

Hi sajee

Try to rename/remove handlers.json and delete mimeTypes.rdf when present in the Firefox profile folder with Firefox closed to reset all file actions.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

That worked. Thanks cor-el.

Cor-el's suggestion worked with viewing a PDF statement on CreditCardCompany1's site. But, as before, I have "Preview in Firefox" set for PDFs. Yet, when I click to view a PDF at CreditCardCompany2's site, I get a dialog box asking whether I want to "Open with Preview (default)" or Save File. Is there some way I can always view the PDF in Firefox by default?

Hi sajee, this is caused by the server sending an extra header:

Content-Disposition: attachment; filename="blablah.pdf"

There are extensions to override the header so that the file can open "inline". For example:

• https://addons.mozilla.org/firefox/addon/display-inline/

I also have it as a feature of my extension (when the extension is listening to requests, a menu drops down from the button which lets you select the option):

• https://addons.mozilla.org/firefox/addon/content-type-fixer/

I added your extension jscher2000 and it works as advertised. Thank you.

jscher2000: On the American Express site (the 3rd credit card site I visited), when I click on the PDF statement, nothing happens when your extension is set to "Allow viewing in a tab". If I set your extension to "As set by server", I get the FF dialog to Open or Save the file. Any idea what's going on?

sajee said

jscher2000: On the American Express site (the 3rd credit card site I visited), when I click on the PDF statement, nothing happens when your extension is set to "Allow viewing in a tab". If I set your extension to "As set by server", I get the FF dialog to Open or Save the file. Any idea what's going on?

No idea. Does the Log show anything strange for that PDF request modification versus the others? Maybe I'll have to remember my AmEx password and try it out.

You can check the server HTTP response headers in the Network Monitor.

• "3-bar" menu button or Tools -> Web Developer
• https://developer.mozilla.org/en-US/Tools/Network_Monitor