How to Remove the PDF.JS PDF Viewer Extension in Firefox

If you’re unhappy with Firefox’s new PDF Viewer, here’s how to get rid of it …

Before I take a look at how you can remove the PDF Viewer extension in Firefox, I’d like to spend a moment talking about why it is necessary to write about it. Add-on removals should be straightforward operations after all. The big issue here is that you can’t remove add-ons installed by third party software from within Firefox. And third parties in this regard also means Mozilla, if the company decides to add an add-on to Firefox automatically. While you can disable those add-ons, you can’t remove them.

If you are running a Nightly version of the browser, you have probably noticed the new PDF Viewer in the add-ons manager. The add-on can be enabled or disabled, but not removed. The same may be true for other add-ons that have been installed automatically by third party software. Security software is known for this for instance, as are application installers that come bundled with adware.

pdf viewer no remove

Most extensions that you have installed in Firefox, regardless of whether they are enabled or disabled, are stored in the user’s profile folder on the hard drive. It is not that difficulty to go there right away, for instance by clicking on Firefox > Help > Troubleshooting Information, and there on the Show Folder button next to Profile Folder.

The very same page lists the installed extensions, and their ID, which you may need for identification purposes, as some extensions use the ID, and not their name, as their folder name.

When you browse the installed extensions in the profile folder, you will eventually come to the conclusion that the PDF Viewer extension is not listed there. While you find all extensions in the folder that you have installed by yourself, you won’t find the majority of add-ons there that have been installed by third parties.

firefox pdf viewer extension

To find the PDF Viewer extension folder, you need to look elsewhere. Instead of going through all possible locations, I’d like to point you in the right direction right away. You find PDF Viewer listed in the installation directory. Here is a short list of the default installation directories.

  • Windows 32-bit: C:\Program Files (x86)\Mozilla Firefox\
  • Windows 64-bit: C:\Program Files\Mozilla Firefox\
  • Linux 32-bit: /usr/lib/firefox-<version>
  • Linux 64-bit: /usr/lib64/firefox-<version>
  • Mac /Applications/

Keep in mind that these folders may differ if you have installed a different release channel.

Open the folder on your system and the extensions folder within as well. Here you find uriloader@pdf.js.xpi, the PDF Viewer extension.

I suggest you backup the extension first before you remove it from the browser just to be on the safe side. Please also note that you need to close the browser first, before you can remove it as it is otherwise marked as in-use by the operating system (at least on Windows).

You will notice that PDF Viewer does not appear any longer in the Add-ons Manager once you have removed it from the local drive. Check out How To Uninstall Firefox Add-ons With No Remove Option for additional information about the process and locations that add-ons may be installed by third parties.

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