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How to get Firefox to display pdf file in browser (Win 7, FF 19.0, AA 10.1.6, IE 9)?


After Firefox updated to version 19, when I tried to view a pdf file, the file appeared in a strange new viewer. Seemed to work OK, but I was concerned (didn't know that it is apparently a new feature of FF 19), and wanted the Adobe viewer back.

After a few minutes of viewing in the FF pdf viewer, a message appeared that said something like-- This viewer may not be displaying the document correctly. Would you like to use Adobe Acrobat instead?-- I clicked yes.

Now, when I click a link for a pdf file, it will either open automatically in Adobe Acrobat (windows application, not viewer within FF), or I'll get a dialog that asks whether I want to save the file or use Adobe Acrobat to open it.

I have followed the instructions here:


Including: http://support.mozilla.org/en-US/kb/view-pdf-files-firefox-without-downloading-them



Delete the mimetypes.rdf file

Delete the pluginreg.dat file

Let me know if you think I've missed any info that would be helpful. Now that I know the new PDF viewer is FF native, I wouldn't mind trying it out.



repair of Adobe Acrobat

If I start IE and click a pdf link within IE, I can view a PDF file within IE, but who wants IE?

Chosen solution

OK, I guess I'll try an uninstall-reinstall of FF and Adobe and any other PDF readers

Read this answer in context 2

Additional System Details

Installed Plug-ins

  • Shockwave Flash 11.6 r602
  • Adobe PDF Plug-In For Firefox and Netscape 10.1.6
  • Next Generation Java Plug-in 1.6.0_39 for Mozilla browsers
  • NPRuntime Script Plug-in Library for Java(TM) Deploy
  • VLC media player Web Plugin 2.0.2
  • LabVIEW 2012 Netscape Plug-in for Win32
  • Nitro PDF Plug-in for Firefox and Chrome
  • LabVIEW 2011 Netscape Plug-in for Win32
  • 5.1.10411.0
  • LabVIEW 2010 Netscape Plug-in for Win32
  • LabVIEW 9.0 Netscape Plug-in for Win32
  • IMAQ 1.0 Netscape Plug-in for Win32
  • The plug-in allows you to open and edit files using Microsoft Office applications
  • Office Authorization plug-in for NPAPI browsers
  • LabVIEW 8.2 Netscape Plug-in for Win32
  • LabVIEW 8.6 Netscape Plug-in for Win32
  • LabVIEW 8.5 Netscape Plug-in for Win32


  • User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:19.0) Gecko/20100101 Firefox/19.0

More Information

  • Top 10 Contributor
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2043 solutions 8897 answers

Helpful Reply

hello, if you want to switch back to the plugin you've used before to view pdfs just go to firefox options > applications & define the default action for the portable document format (pdf).

Question owner

Hi madperson,

Thanks, but setting the options to define the default action for the portable document format is among the things listed that I have already tried. Modifying the default action only lets me select whether I save the file or open it with Adobe Reader (not in browser). Selecting the plugin doesn't seem to make the plugin work.


  • Top 10 Contributor
  • Moderator
2043 solutions 8897 answers

ok, in this case it's maybe also necessary to totally switch off the inbuilt pdf veiere - enter about:config into the firefox location bar (confirm the info message in case it shows up) & search for the preference named pdfjs.disabled. double-click it and change its value to true.

Helpful Reply

Hi madperson,

It seems like there is some progress. After setting pdfjs.disabled to true, when I click on a pdf link, it still only asks me if I want to open the file with (application list) or save the file. However, when I look at the options dialog>applications, the selection for pdf documents changed from use plugin to use Adobe Acrobat Reader (not plugin). I scrolled through the selection list, but the Adobe plugin was not listed. However, when I look at the add-ons screen, the Adobe Acrobat Reader plugin is listed at the top. So, it seems like the plugin is installed, but firefox doesn't know it's there...somehow.

How do I uninstall the Adobe Acrobat Reader plugin and re-install? Can I just do that? Or, do I need to uninstall/reinstall the entire Adobe Acrobat Reader application?



Chosen Solution

OK, I guess I'll try an uninstall-reinstall of FF and Adobe and any other PDF readers