If you're referring to XF2, then old XF1 add-ons under the library directory are no longer used (in fact, nothing in the library directory is used if you've upgraded to XF2).
For XF2 add-ons, the add-on files are all stored under the src/addons directory, and the folder names match the add-on IDs of the add-ons, so that should make it easier to identify them.