Type about:preferences#applications<Enter> in the address bar. What is the information for those type files?

Did you want to show the file in Firefox, or another viewer?

When I enter about:preferences#applications <Enter> in the address bar, then for PDF it shows: pdf File (application/x-download) ... Use Adobe Acrobat Professional

pdf File (application/x-pdf) .... Use Adobe Acrobat Professional

Portable Document Format (PDF) ... Save File

I would like all PDF's to open in Adobe Acrobat 8 Professional. Right now none of the PDF's open at all, so opening in Firefox or any other viewer would be preferred over not showing up at all.

You can change the setting by clicking the button at the far right.

It does not seem to make any difference whether the "Action" on all 3 of the above pdf Content Types are set to "Always Ask" or "Use Adobe Acrobat Professional" .... when I click on a pdf link it just opens a blank page. Is this problem inherent to newest/current version of Firefox. It seems others have experienced same problem?

See also this image regarding PDF Add On being incompatible.

That last picture said to try PDF Viewer.

There are many viewers here; https://addons.mozilla.org/en-US/firefox/search/?q=PDF%20Viewer.

OK, I selected: Google Docs Viewer (PDF, DOCX, PPTX, XLSX, etc...) View publicly-accessible PDF, DOCX, PPTX, XLSX, among other files online with Google Docs by only 2 clicks. Click as usual for your default viewer. Support bookmarked URLs. Security and your explicit viewing intention are always honored. Rated 4 out of 5 stars (58) 52,087 users Then clicked on Add to Firefox. It does now show up in Add-ons - Extensions.

But ... when clicking on a PDF link, I still only get a blank page. (some of the other pdf viewers indicated that they were incompatible with Firefox 35, so I did not try any others).

I assume that Mozilla does not have Customer Service / tech support, correct?

Robert5280 said

I assume that Mozilla does not have Customer Service / tech support, correct?

In a manor of speaking. It's us.

I've called the big guys to help you. Good luck.

I uninstalled Firefox, and then re-installed Firefox. Now it opens the PDF files as "Preview in Firefox". Thanks for your various suggestions.

Glad to help.

Please flag your last post as Solved Problem so other will know.

Actually the Solution .... Problem Solved was: "I uninstalled Firefox, and then re-installed Firefox. Now it opens the PDF files as "Preview in Firefox"."