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Installed Plug-ins

Adobe PDF Plug-In For Firefox and Netscape 10.1.6 Adobe PDF Plug-In For Firefox and Netscape "9.5.5"
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Adobe PDF Plug-In For Firefox and Netscape: Adobe Reader Version Version 2015.017.20050 Note: Other Software is offered in the download.

Fred, thank you, and that makes sense. But, how do I delete the old version of the plug in?

Type about:plugins<enter> in the address bar. Now search for the plugin.

Example; Adobe Acrobat File: nppdf32.dll,nppdf32.dll Path: C:\Program Files (x86)\Adobe\Reader 11.0\Reader\browser\nppdf32.dll,C:\Program Files (x86)\Adobe\Reader 11.0\Reader\AIR\nppdf32.dll Version: 11.0.9.29 State: Enabled Adobe PDF Plug-In For Firefox and Netscape 11.0.9

This will show you the path to that program. Copy the Path Only. Also, note the name of the file, and remember it. Now Close Firefox. Open your file browser and paste the path in the address bar. Find the file, and delete it. Now you can restart Firefox. Warning ! Remember to delete the right program.

To be safe, remove all of them. Then install the current.

The Adobe Reader X series is no longer getting updates. I suggest the Adobe Reader XI series (just because the interface in the newest design is a significant departure).

You can choose the XI series installer by using this page:

https://get.adobe.com/reader/enterprise/

That will give you an intermediate version such as 11.0.10.

To get the latest security patches, after the installation, open Adobe Reader and use Help > Check for Updates.

FYI, the last update was 11.0.17 (this page has updaters in case you need to download one instead of using the internal Check for Updates method): http://www.adobe.com/devnet-docs/acrobatetk/tools/ReleaseNotes/11/11.0.17.html