You can use a mozilla.cfg file in the Firefox program folder to lock prefs or specify new (default) values.

Place a local-settings.js file in the defaults\pref folder where also the channel-prefs.js file is located to specify using mozilla.cfg.

pref("general.config.filename", "mozilla.cfg");
pref("general.config.obscure_value", 0);

These functions can be used in the mozilla.cfg file:

defaultPref();	// set new default value
pref();		// set pref, allow changes in current session
lockPref();	// lock pref, disallow changes

See:

• http://kb.mozillazine.org/Locking_preferences

• http://mike.kaply.com/2012/03/16/customizing-firefox-autoconfig-files/
• http://mike.kaply.com/2014/01/08/can-firefox-do-this/

You need to set the related plugin.state pref(s) to 2 to always activate a plugin.

• lockPref("plugin.state.npmcffplg", 2);

• plugin.state (0:Never Activate; 1:Ask to Activate; 2:Always Activate)

Thank you kindly. Worked like a charm.

would it be possible to "Always Activate" certain plugins for certain Websites? Or is it an all or nothing setting?

Thanks in advance for your assistance Ed

You can inspect and manage permissions for the domain in the currently selected tab via these steps:

• Click the "Site Identity Button" (globe/padlock) on the location/address bar
• Click "More Information" to open "Tools > Page Info" with the Security tab selected
• Go to the Permissions tab (Tools > Page Info > Permissions) to check the permissions for the domain in the currently selected tab

Clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, passwords, and other website specific data like enabled plugins.