In der Safari Developer FAQ gibt es zu der Frage 11: What type of plug-ins does Safari support? folgende Antwort:

Safari uses Netscape-style plug-ins. For more on writing plug-ins for Safari, see Apple's Technical Note on Browser Plug-ins for Mac OS X and Netscape's definitive Plug-in Guide.

A very simple Sample Plug-In is available, however you will need the appropriate header file "npapi.h" from Netscape to build the project yourself.

Ich hoffe, ich benötige diese Informationen zeitnah.