[Firefox] How to disable Firefox’s native PDF reader/viewer in Firefox 19 and higher

As mentioned earlier, starting in Firefox 19, Firefox has a native PDF reader. This means Firefox can view PDFs without you having to install a third-party add-on or program. Firefox’s PDF viewer is enabled by default. The issue is, some people may prefer their third-party PDF readers over Firefox’s built-in viewer. This article shows you how to disable Firefox’s native built-in PDF viewer and change it back to your third party program.

Take note this tip is divided into two parts. The first part shows you how to make Firefox use the third-party PDF reader you have installed instead of Firefox’s built-in PDF viewer. The second part shows you how to disable Firefox’s built-in viewer completely. The difference is, with the first part you don’t disable Firefox’s PDF viewer — you just don’t use it. With the second part you completely disable the viewer.


The process of changing back to your other PDF reader is actually pretty simple. Do the following:

  • Go to Firefox ‘Options’. Depending on your Firefox settings, it may vary how to get to ‘Options’ but most people should be able to get there by clicking the orange ‘Firefox’ button in the top-left corner, going to ‘Options’ and then ‘Options’ again.
  • Once in ‘Options’, go to ‘Applications’.
  • At ‘Applications’ type “pdf” in the search box (without the quotes):


  • Once you type “pdf” in the search bar, you should see a PDF entry show up. Click on the drop-down menu and select the PDF reader/viewer that you want to use:


  • Finally, click ‘OK’:


Done! Now Firefox will display PDFs in the PDF reader/viewer of your choice and not Firefox’s built-in PDF viewer.


This one is a bit more tricky and involves the use of about:config. Do the following:

  • Type in ‘about:config’ (without the quotes) in your address bar and press ‘Enter’ on your keyboard.
  • You will be prompted with a warning that says “This might void your warranty”. Read the warning and click ‘I’ll be careful, I promise’.
  • Now type in “pdf” (without the quotes) in the search bar at the top:


  • Once you type “pdf”, the results will be filtered to only show PDF-related results. Find ‘pdfjs.disabled’ and double left-click it so that it says ‘true’ for ‘Value’:


  • Done!

You can close the tab/window. Once you have set ‘pdfjs.disabled’ to ‘true’, Firefox’s native PDF viewer has been disabled. There is no save button to hit — all changes are saved in real-time.



Related Posts


Leave a Reply

Your email address will not be published. Required fields are marked *


  1. Martin

    Thanks for the tip! The build-in reader is worthless – I have yet to see one pdf that was correctly displayed – some even loose all the text! After the build-in reader was finished, I still had to open the pdf in Foxit Reader to actually SEE the pdf – which means the whole procedure took me twice the time it took me before this change. Mozilla, please leave this kind of nonsens to I.E., from them we are used to it.

  2. Paul D

    FWIW, here’s the full rundown on how I handle PDFs. I have both Sumatra and Nitro installed. Sumatra is my default reader for documents on my hard drives, because it’s just so FAST, and I still have Nitro available for anything more complex (ie, filling in forms). Within Firefox I use Nitro, because the popup toolbar is so useful.

  3. David Roper

    I saw Sumatra mentioned and tried it. Wow is it fast. I was running Foxit because others were running it. Ho Hum. Tried the rest including FF plug in, Nitro (would not do what it promised, ie chop PNG image out of a PDF) and right now I’m settled on Sumatra. It’s so fast, the image on my laptop appeared as the key I pressed was released, Just WOW!

  4. mukhi

    [@mukhi] aah, i think i messed up with typing the last time (meh, no edit), it should read:
    my sumatra is portable only. no probs with that. when i did not disable FF reader, the reader was downloading PDFs as redirect.do, so i had to disable FF reader so that i didn’t have to rename the file as file.pdf.

  5. mukhi

    [@Paul D] well, i have used foxit, and it’s a great reader (faster than adobe, portable, and tabbed PDF reading functionality) except for the fact that it has some problem for PDFs opening in browser. sumatra is very good in the sense that it can read whole bunch of files, specially, many different ebook formats.

  6. Juan Pantera

    Thank you so much!!! Your post has been very usefull. I think Firefox is a great software, but changes like pdf.js aren’t a good idea. After use this plugin, I prefer FoxIt or Acrobat definitely.

  7. WildCat

    If you are running a Nightly version of Firefox and want to completely rip it it out then check out http://www.ghacks.net/2012/05/15/how-to-remove-the-pdf-js-pdf-viewer-extension-in-firefox/

    Got another add-on you can’t remove? Well you’re in luck! The author, Martin Brinkman, who wrote the above article has another interesting article called: How To Uninstall Firefox Add-ons With No Remove Option. You can check it out by clicking the link for it in the previous article or by going here: http://www.ghacks.net/2012/02/04/how-to-uninstall-firefox-add-ons-with-no-remove-option/ (NOTE: I would classify this one for the more ‘serious PC tinkerers’ out there. And ALWAYS REMEMBER… BACKUP your data!!! )

    If you’re curious as to what all is running in your FF profile folder, or you need to find your profile folder, just do the following…

    In Firefox 3.6 and above, you can open your profile folder directly from the Firefox Help menu, as follows:

    In the Firefox Button or menu bar, click “Help” and select “Troubleshooting Information”. The about:support page will open.
    At the TOP of the page, under “Application Basics”:
    On Windows and Linux, depending on Firefox version, click on “Show Folder” (Windows) “Open Directory” (Linux) or “Open Containing Folder”.
    On Mac OS, click on “Show in Finder”.

    Another nifty trick… The Firefox menu bar contains the File, Edit, View, History, Bookmarks, Tools, and Help menu items. On Windows, the menu bar may be hidden. You can press the “Alt” key to temporarily show a hidden menu bar.

  8. osreinstall

    Type in about:config in url bar.
    click yes never to screw it up.
    In the search type in PDF to narrow your search.

    set pdfjs.disabled true by double clicking.

    You got that so far.

    Now right click on the other entries and click reset to default values except the pdfjs one. The next time you open up about:config and type in pdf you should have 4 entries. pdfjs will be bold the non-default and the other 3 will be plain which is the default. This does not screw up the browser for it clears out the prefs.js file in the profile. I have re-enabled it and all entries come back. Then I repeated the process to disable it. I don’t think it is necessary, but I like things at default value if not using them.

  9. PixelWizard


    Thanks for confirming my hunch. I certainly prefer PDF-Exchange to the new native reader (speed advantage or not). Just for starters, PDF-Exchange has text searching capability.

    But could you explain ‘I also reset every line to default’? Every line of….? Reset how?

  10. osreinstall

    Yes it does, considerably. I have a system that scores between 210-215 with SunSpider’s JavaScript Benchmark when Firefox’s built-in PDF viewer is enabled and PDFExchange disabled. I disabled Firefox’s built-in PDF viewer plus I also reset every line to default and then re-enabled PDFExchange and ran SunSpider JavaScript Benchmark. The score was between 190-195. That is 20 points lower on the average or a 10% increase in speed. Firefox’s PDF viewer will not render the fonts correctly and in some cases not render them at all with just lines instead of text in certain PDF files. Firefox has some serious coding to get this to work properly.

  11. we

    Unfortunately, Firefox’s viewer is not great. It constantly says that the PDF may not be displayed correctly, and the “Page Fit” option doesn’t work. Page Up and Page Down should change to the next page exactly when using this option, and Firefox is just a little off.

  12. Aardvark

    Thanks for this information. I was going to stick with Firefox’s PDF viewer but this morning I went to view a PDF and a warning popped up in Firefox that it might not render properly and to choose an alternate viewer. I thought “screw that”, I want Adobe back. It never told me to try another viewer.

  13. AFPhy6

    Thanks for that possibility. I was hoping that there was some “difference from starting configuration” utility, but I could do what you suggest, and then compare the new prefs.js file with the one I have right now… Probably a regular file-file compare utility will do just fine.

  14. AFPhy6

    [@Ashraf] (or anyone else)

    I have changed quite a few “about:config” settings over time. Thus far, I have not broken anything or been unhappy about any of the results. However, I keep having a nagging thought that I might desire to reverse one or more of those settings.

    Does anyone know of a way to locate the “original settings”, or alternately, a way to see changes that I have made to “about:config” over time?

  15. David Roper

    I detest Acrobat Reader updating all the time, I use a simple program like you use Nitro, but If I did and could disable it wouldn’t certain programs check (mostly Government forms) check first and dissallow forms to be printed or downloaded. Sorry if I just set the “record” for a sentence length on dotTech.

  16. Ashraf
    Author/Mr. Boss

    [@PixelWizard] Honestly, I don’t know. And, to be completely honest, making Firefox’s built-in reader not be the default does not disable it — it just isn’t used. If you want to completely disable it, you need to make an about:config modification. I should update the article to reflect that.

    You are welcome.

  17. PixelWizard

    Thanks – I do understand this setting change. Until now I had PDF-XChange Viewer opening the pdf files on demand, as a standalone system-wide default (i.e, without any browser plug-in).

    My question: does disabling the new native pdf reader lighten Firefox’s memory usage or speed up the browser launch, or anything of that nature?