In OS Lion which is the plugin installation folder
In OS Lion, where do I install third part FCP Pro X plugins
Final Cut Pro X, Mac OS X (10.7.1)
They're actually Templates, not plugins. Plugins will come with their own Installer. Temnplates you install yourself. Movies > Motion Templates. You'll have to know what type of template it is, and put it into the appropriate folder. In there, make a folder called Custom, so they're kept organized away from your stock templates.