Great! Glad that the PDF add-on (I assume pdf.js) is working well for you.

Yep it is pdf.js

https://github.com/mozilla/pdf.js/

If you want to use Adobe Acrobat, you can just change the preference that was messed up:

Go into Firefox > Preferences > Applications and look for "PDF file"

Next to that, select use Adobe Acrobat (or use Preview) rather than Adobe Acrobat NPAPI 10.1.3

Adobe's NPAPI plugin doesn't work in 64-bit Firefox ... there's probably a bug where the Adobe Reader update is setting that preference.

(From: https://support.mozilla.org/en-US/que.../925239.)

I don't have a "PDF file" but rather an "Adobe Acrobat PDF Document" entry in my Application Preferences. When I change that entry (and the other two "Adobe Acrobat ..." entries) to "Use Adobe Reader (default)" from the NPAPI 10.1.3 plugin, I get the same behavior (yes, I restarted Firefox). A window pops up when I attempt to view a PDF document, but Adobe Reader never comes up and I never see my document.

Any idea why? Everything worked fine with the previous (10.x) version of Firefox.

Are you sure you have the same problem? This is specific for OSX users who recently updated Adobe Acrobat (and possibly Reader) and was caused by this update. If you have a different problem, can you please start a new post so that it's clear?

Well, the symptoms are the same. I'm running Mac OSX 10.7.3, Firefox 11.0 (recently upgraded and haven't been able to view PDF documents since the upgrade), and prior to my changing the setting for the "Adobe Acrobat PDF Document" file type, had been using the "Adobe Acrobat NPAPI 10.1.3" plugin to handle this file type.

In any case, I still can't view PDF documents in Firefox (but everything works fine on the same machine using Chrome).

Oh, forgot to mention, I did just recently update Acrobat Reader too -- so it might have been the update of Reader, rather than the update of Firefox, that broke PDF files. I didn't pay much attention as to exactly when PDF files stopped being able to be rendered in Firefox.

Cww, Very helpful thank you!

For those who haven't a clue about these things (like me), I followed Cww's instruction but instead of finding "PDF File", I found ADOBE PDF DOCUMENT and I selected USE ADOBE READER (DEFAULT).

It worked!

Problem solved!

I did what Lili2012 suggested, as Cww instructed....Although with a little bit of a twist...

I clicked on Firefox, clicked Preferences, clicked Preview Document (application/pdf), choose Use Adobe Reader (default)

That solved this mystery

Tip for those who are as computer-challenged as I am: If you want to fix the problem by using cww's solution--going to Firefox Preferences/Applications and selecting "Use Adobe Acrobat Reader (Default)" instead of "Use Adobe NPAPI Plug-in"--you may be hunting for "Adobe PDF" at the top of the list. In my Preferences, however, it's listed under the "P's": "Portable Document Format." (Go figure.)

Switching to "Use AAR (Default)" worked fine for me, once I realized that I had to use the search box because my Preferences/Applications window doesn't look like the screen shot in the documents here. (The 32-bit solution did, too; disabling the NPAPI Plug-in didn't.)

I also had to disable the Acrobat plugin 10.1.3 in addition to choose to open with Reader or preview in order for it to work properly

I still do not have this working. I'm now running Firefox 12.0. I do not have an application/pdf or PDF file in my Preferences/Applications/Content Type list. The first three items read "Adobe Acrobad FDF document", "Adobe Acrobat XML Data Package File", and "Adobe Form Client Data File". All are mapped to "Use Adobe Reader (default)". I see no other content types (or mime types) that reference pdf.

Whenever I click on an PDF link, I see the URL in my address bar, but I have a blank page. I don't see how to add Content Types to the list. If I download a PDF file, and try the "Open file..." menu item, navigating to the directory containing the PDF, when I click on the PDF file, I get the same behavior. It is as though Firefox doesn't know how to handle PDF files any more. I've verified when I click on PDF links from web servers, that the mime type is application/pdf, but nothing is displayed.

I've staved off the switch to Chrome for the last few years because of Firefox' URL tagging feature, but PDF files are so much of my life that I've switched to Chrome until I can get a resolution.

Well, although this thread was not helpful to me, I found another one which was: https://support.mozilla.org/en-US/questions/925055#answer-325683.

In short, the fix is to disable or remove the Adobe Acrobat NPAPI plugin from the Tools|Add-ons menu. Manipulating entries (existent or non-existent) in the Preferences|Applications menu did not help.

Folks, I posted the original question. Use this EXTENSION it works like a charm and is super fast.

https://github.com/mozilla/pdf.js/

The pdfs documents open as a tab in the browser. This

I disabled Adobe Acrobat NPAPI plug in.

Same problem as all of you except it was more common to eswenson's issue. In the added as tk_det added its best to diasble the Adobe NPAPI plug-in and install the Stable Version: https://addons.mozilla.org/en-US/firefox/addon/pdfjs

My problems are sorted for now and I can keep using Firefox with pdf.

I had exactly the same problem. . Problem started suddenly about 2 weeks ago. I had the same problem with Safari. Adobe helped me solve in Safari by dragging the AdobePDFViewer.plugin from the Internet plugins folder onto the desktop. I totally uninstalled Firefox including deleting profile, then reinstalled. Still didn't work until I switched action for Adobe PDF in Applications preferences for use Adobe Acrobat Pro. Guess that only works if you have Acrobat Pro.

I had this same problem yesterday trying to download my bank's statement. I used the help here and changed the Firefox PDF preference to Save File. Then when it downloaded. I just changed the name with a .pdf. I have a macbook pro running 10.6.8 and Firefox 12.

@eswenson: I too was confused by the several Adobe Acrobat entries that appear in the Application preferences, as they are misleading. Instead you need to look for an entry that says "Preview Document" which is further down in the alphabetically sorted list and change that to "Use Adobe Reader" in the second column.

@martinmiller2: Thanks. However, in my case, this really wasn't the issue. While I didn't have an entry for Preview Document, I did have one for "Preview.app Document (application/pdf)." This entry, however, was (and still is) set for "Always Ask". My problem turned out to the be Tools|Add-ons "Adobe Acrobab NPAPI..." plugin, that had to be disabled.

A nice troubleshooting guide for FF and Acrobat is here: http://www.pdfshareforms.com/pdf-forms-on-mac-with-firefox/