Using NPAPI Plugins within Firefox Version 43 or later

Issue

Mozilla announced on its blog that Firefox would stop supporting plugins based on the Netscape Plugin Application Programming Interface (NPAPI) architecture by the end of 2016.

New platforms such as 64-bit Firefox for Windows will launch without plugin support.

Workarounds

In Firefox, it is possible to disable the add-ons signature enforcement. After that, all your add-ons will continue to work as before.

Here is how you can disable it.
Open a new tab and enter the following text in the address bar:

about:config

Confirm that you will be careful if a warning message appears for you.
Enter the following text in the filter box:

xpinstall.signatures.required

To disable the feature, set this option to false.

Optional this behavior could also be set by adding the following to prefs.js:

user_pref("xpinstall.signatures.required", false);

More at:
https://wiki.mozilla.org/Add-ons/Extension_Signing 

After that, all your disabled non-signed extensions will start working in Firefox.
However, this solution is not permanent.
With Firefox 46 or some later version, Mozilla might remove the "xpinstall.signatures.required" option.

So you might want to consider the following alternatives:

Mozilla offers an Extended Support Release (ESR) based on an official release of "Firefox for desktop" for use by organizations including schools, universities, businesses and others who need extended support for mass deployments.

You can read more about this here:
https://www.mozilla.org/en-US/firefox/organizations/faq/ 

Applies to

• All Kofax E-signature products