How-To Geek

How to Enable Firefox’s Built-in PDF Reader


Firefox 15 includes an all new PDF reader built into the browser–for those of you wondering, that means you can finally disable the Adobe PDF Plugin and uninstall it once and for all.

Note: obviously if you need to access more advanced PDF features, you’ll still need the Adobe plugin. For most of us, however, the built-in viewer is fine, or you could download PDF files and read them in the offline Adobe Reader.

Enabling Firefox’s Built-in PDF Reader

Open Firefox and navigate to about:config.


This will bring up a sarcastic warning telling you that you might void your warranty, just click the “I’ll be careful, I promise!” button to move on.


Now you will need to search for:



When you find it, right click on it and select Toggle from the context menu.


Next you will need enable the actual PDF Reader feature, you can do this by searching for:



That’s all there is to it, you can even drag PDF files on your local machine on t0 the Firefox windows to view them!


Note: As pointed out in the comments, you will need to disable the Adobe addon after you have completed this.

Taylor Gibb is a Microsoft MVP and all round geek, he loves everything from Windows 8 to Windows Server 2012 and even C# and PowerShell. You can also follow him on Google+

  • Published 09/7/12

Comments (35)

  1. YaY

    Finally, I can get rid of that crappy Adobe Reader off my system!

  2. Peter

    Why don’t Mozilla add an entry to Options to turn this on? Seems crazy that non-Geeks have to go through that process in order to enable the function. My gran won’t be able to do it, I know.

  3. Javier

    You can go to and install it as an add on (for all the non geeks)

  4. Jack Weekes

    You might also need to go into “Add-ons” the “plugins” and disable Adobe Reader from the list else it might still use that for default, as it did for me. I know it’s mentioned at the top but not in the instructions and might confuse a few people. Nice tip though!

  5. Tim

    Cool! No more clunky plugins and external apps.


  6. TechnoGeek

    Is it really necessary to turn on in-content preferences to use the pdj.js viewer? I think the in-content preferences are completely separate and should be in a separate article.

    @Peter: I think pdf.js is currently still being tested and unfinished, so it’s not easily visible by default yet.

  7. Harry Verstandig

    When I select and click on the ‘Toggle’ option, all it does is change the Value from true to false. What am I doing wrong??

  8. Taylor Gibb

    @Harry thats correct, the option pdfjs.isDISABLED is set to true, hence we need to set it to false to ENABLE the plugin. Sorry for the caps, its the best way i could get the point across =)

  9. StevenTorrey

    What if I don’t want to use Mozilla?

  10. Taylor Gibb

    @Steven then use Chrome XD

  11. Penn Boy

    What happens/step to take if browser.preferences.inContent doesn’t exit in config??

  12. cam2644

    Good tip.Thanks

  13. TheFu

    Anyone know if this is this any safer than using Adobe Acrobat?

    We all know not to use Adobe-anything unless it is making money, right?

  14. Laterus

    Doesn’t seem to work on me.. Did it thrice and all it does is show the download options whenever I drag PDF files onto the FF browser.

  15. aisamji

    Same for me.

  16. aisamji

    Never mind. I tried restarting Firefox and it works now.

  17. B Pratt

    Lord, I gave up on Adobe reader years ago and have been using Foxit. This works just fine for me.

  18. r

    I use Acrobat Pro, super program & very versatile.
    Foxit is a good free one.

  19. Cornflower

    While I appreciate “Toggle”, it is non-intuitive whether the graphic was in initial or ‘after-toggle’ position.
    I have at times encountered one or more settings already in the end-state, and in these conditions, one should not toggle the setting.
    To clarify, then, I suggest always including the end-state text as well, i.e.,

    It should now be True:
    browser.preferences.inContent = True

    It should now be False:
    pdfjs.disabled = False

  20. Dic

    Nitro Reader for me.

  21. paleolith

    Sumatra works great for me.

  22. Ezaafi

    thanks for this tip.

  23. minimoto

    I didn’t work for me at first but then i searched for “pdfjs” then reset (right-click) all those values to their default; except for “pdfjs.disabled” of course. Then restart Firefox [16.0].

  24. Dig-a-Ling

    You mean to say that there are people actually gullible enough to install – and use – Adobe Reader?!


    so nice!

    i recently used chrome build-in pdf reader, this is a very good and useful article.

  26. Taylor Gibb

    @Cornflower You raise a good point, what if someone had already modified that setting, then they toggle it to the wrong setting. I will remember this for next time. =)

  27. Paul D

    I’m with Dic and paleolith. I have Sumatra as my default reader (small, fast and lightweight) and Nitro for some advanced features. Foxit has grown to be nearly as big and clunky as Adobe Reader.

    As for r, Sure Acrobat Pro is good. It’s also bloody expensive.

  28. Paul B.

    For a superb full-featured alternative to adobe, try pdf-xchange, which also has a browser plugin.

  29. Shirley Stasko

    I play games in facebook (example-Castleville). It doesn’t matter if I used Firefox,IE or Google I need the adobe flash plugin and yet everything I do it crashes. Is there a way around this? Gets very frustrating when trying to play a game.

  30. r

    @Reader : have to agree, Acrobat X Pro is totally overpriced for most.
    However, I got it with CS5 Master Collection. So, there really is no reason for me to use an other.

  31. Seenu

    gr8 hack..loved it
    never thought my firefox would be a pdf reader

  32. Advait Panchal

    Its a barebones PDF reader but perfect for me

  33. Luis A Ramos Jr

    Nice hack and Now I can get rid of Adobe Reader if I want to.

  34. JDT

    You need to do one more thing to make it work:-

    In Firefox, go to options>applications and for content type “Portable Document Format (PDF)” select “Preview in Firefox”.

    Then it works. Seems OK so far!

  35. djinks

    Thanks for the clear instructions. The toggle was consusing me also. Didn’t know if the images were before or after.

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