How to enable built-in PDF Viewer in Firefox 15

Mozilla sometime earlier released the newest version of its open-source, cross-platform web browser – Firefox 15. The browser runs with reduced memory usage for add-ons, has a new JavaScript debugger and more. It is compatible with both, 32-bit and 64-bit versions of Windows OS.

Also, Firefox 15 features a built-in PDF Viewer but it is not enabled by default. So, this becomes our topic of discussion. In this post, I will guide you through the process of enabling the built-in PDF Viewer in Firefox 15.

Why has the feature not been enabled by default? Because, the PDF Viewer is still in the Beta state and therefore you have to manually enable it.

Enable built-in PDF Viewer in Firefox

Open Firefox browser and in the address bar type the following – ‘about: config’ and hit ‘Enter’.

Instantly, a warning will be displayed on your computer screen with the following message – This might void your warranty. Changing these advanced settings can be harmful to stability, security and performance of the application. Just ignore the message and hit ‘I’ll be careful, I promise!’ button.

Once you do it, a big list will be visible to you.

In the search box, type ‘Browser.preferences.inContent’.

After you find the same address in the list, right-click on it and choose the Toggle option. This should change its value from ‘False’ to ‘True’.

Do the same for other address – pdfjs.disabled! Type pdfjs.disabled in the search box.

When found, right-click on the option and choose ‘Toggle’ again. This will change the value from ‘False’ to ‘True’.

That’s it!

The Firefox built-in PDF Viewer has now been enabled. Simply visit a linked PDF document of any website and it should open in the browser. See the screen-shot below.

Firefox’s built-in PDF viewer is just a basic PDF files viewer for Firefox browser. If you would like to access more advanced PDF features you’ll need the Adobe or Foxit plugin.

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The author Hemant Saxena is a post-graduate in bio-technology and has an immense interest in following Windows, Office and other technology developments. Quiet by nature, he is an avid Lacrosse player. Creating a System Restore Point first before installing a new software, and being careful about any third-party offers while installing freeware is recommended.


  1. howiem

    I was using Sumatra pdf in FF15.0.1 and running the browser in a sandbox (sandboxie). I made the changes per this tip, disabled the Sumatra pdf plugin and restarted Firefox, searched for a PDF file, and tried to open it, but instead of seeing the file open using the Firefox PDF reader, I was offered the save or open with option.
    What I would like to know is whether or not the FF PDF reader has the capability to search a pdf file? I cannot tell from the image above

  2. Beppe

    I clearly read “Find” as a cue text to a text field in the pdf pane…

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