Q: No Audio Plug-In(s) on my mac?

WWhich library did you look un, user or system?

I can give an example as if a user has installed adobe flash player to run it smoothly , we open safari > safari preferences > internet plugins ( check this box ) > plug in settings > adobe flash player > choose as allow & click on done .

And i am not sure about FCP as you have stated in the post .

An apple article may help you : Safari: About Internet plug-in management - Apple Support

DDon't know what's going on. You have another thread that shows you HAVE plugins you shouldn't have.