I'm not sure I understand what you mean with "Firefox opens documents from the Internet as URLs" ?

Are you saving files to your hard drive via an 'open with' dialog and are you trying to open such a file in Firefox ?

Can you elaborate and give more detail about the procedure you use ?

Viewing a website in Firefox, if I click on a file, Firefox returns a link to the file, not the contents.

Same scenario in IE, if I click on a file, IE returns the document. I can later save it as a fil.

Viewing a website in Firefox, if I click on a file, Firefox returns a link to the file, not the contents.

Firefox just shows a link instead of opening the file in that tab or a new tab? What kinds of files have this problem?

Is this about links on a web page or about links on your computer (bookmark or history) ?
Are you talking about loading pages you visited previously from the disk cache ?

Without a clear understanding it is hard to say what is different with Firefox than with IE.

OK, here is an example: If I open this website: www.axisgis.com/gilmantonNH and go to find 401-025 410-025 by entering that in the search. Then click on the property retrieved and a window pops up that says Parcel # 410-025-000 and below that Documents & Links where it says CAI Property Card. Click on that. Firefox returns a URL: GilmantonNH_5192cbda-ffde-41bb-ae8a-08c7beebe8fa rather than simply opening the document. Happens all the time at all sites.

For me, the CAI Property Card link launches a new tab with this in the address bar:

https://www.axisgis.com/Reporting/Reports/GilmantonNH_db69d995-977d-46da-a18d-ca13ffe174f8.pdf

Note: due to the new link filter, newer posters cannot post links to non-Mozilla sites or quote them in reply.

After a brief delay, that PDF then opens in Firefox's built-in PDF viewer in the tab. If you are getting a new tab but that PDF -- or any other PDF -- doesn't display, could you take a look at this setting:

Select the first option for PDFs on the Options page

This used to be called "Preview in Firefox" and now is called "Open in Firefox":

If this option is not available on your Firefox, let us know.

Any difference?

Forgot the article link: View PDF files in Firefox or choose another viewer

I've edited your above reply to fix the typo: 401-025 => 410-025

Works for me here as well with showing the PDF in a new tab

Just to be sure:

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows a purple shield icon at the left end of the location/address bar in case Tracking Protection is blocking content. You can click shield icon for more detail and possibly disable the protection. You can check in the Web Console what content is blocked.

• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop