A new stable version of the popular Firefox browser was released today. This is the first version of the browser which has support for classic NPAPI plugins disabled.

In Firefox 52, the user can turn on NPAPI plugin support using about:config.
Here is how it can be done.

  1. Open a new tab in Firefox and enter the following text in the address bar: about:config
    Confirm that you will be careful if a warning message appears for you.
  2. Create a new boolean option and name it  'plugin.load_flash_only.'
  3. Set the plugin.load_flash_only option to 'false'.
  4. Restart Firefox.

Other links:
Google Chrome V42 disables Silverlight : KBA-35408