Ik heb nog wat gevonden, het moet toch mogelijk zijn op een Mac
Mac:
System-wide script-fu scripts are stored in /Applications/Gimp.app/Contents/Resources/share/gimp/2.0/scripts/. Executable and python plugins are located in /Applications/Gimp.app/Contents/Resources/lib/gimp/2.0/plug-ins/
User-private plugins are stored under $HOME/Library/Application Support/Gimp/2.8/plug-ins/.
NOTE: Check "Preferences > Folders" to confirm your plug-ins directory. On some systems, it may be set to "Library/Application Support/GIMP/2.8/plug-ins/" which is wrong. Fix this by adding a new path and restarting.
Testing the plugin[edit]
To test the plugin, simply open the GIMP and try the plugin. If this plugin makes a certain image type supported, try opening a file of that type. If the plugin is a filter, test it.
Troubleshooting[edit]
If the plugin appears to not be working, be sure that its for your OS and it is for your version of GIMP.
Also, Scheme ( Script-Fu ) plugins (*.scm) and python plugins go in their own respective folder, up one level from the regular plugins directory. Python plugins also require gimp-python.
The Script-Fu directory is something like /usr/share/gimp/2.0/scripts/.