What is the common PDF viewer used by most of the computer users? You will quickly answer it as Adobe Acrobat Reader! But what if I ask, how do you view, open PDF files in Firefox automatically? Hmm.. Not everybody has an answer. Well the geeky technocrat may answer that he uses Adobe Acrobat add-on or some other, to accomplish the above. But with the new stable version of Firefox 15, the add-on nuisance is completely removed.

With Firefox 15, you can enable the built-in PDF viewer, which will automatically open the PDF files in the browser itself. But this option is disabled by default. So you need to enable it to make this feature work properly.

How do you do it?

  • In the Firefox address bar, type about:config (exactly as mentioned) and hit enter.
  • You’ll prompted with a message that says “This might void your warranty!etc. Click on the I’ll be careful, I promise !  button which is below the message. So be careful now onwards on what changes you are making.
  • In the Search: field, type pdfjs.disabled.


  • You should get only one entry for this particular search in the Preferences section below it. Double click this entry to change the Value to false.


  • This enables the built-in PDF viewer facility in Firefox. Now re-start Firefox.

Note : If somehow you have the Adobe Acrobat add-on in your list of add-ons, you need to disable it. This you can do it by going to the Add-ons Manager in Firefox. You can go to Add-ons Manager by clicking the Firefox button at the top left hand corner of the browser and clicking Add-ons on the right side of the pop-up menu that opens up.

Now when you open a link to a PDF file in Firefox, the PDF file will open in the browser window or tab itself.


There are several options with this built-in PDF viewer in Firefox. You can increase and decrease the size of font of the PDF file, add or remove the “sidebar”, go to a particular page etc.

The other advantage with this built-in feature is, this will improve Firefox performance and start-up speed, as we do not require to use any third-party add-on to view PDF files.

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