To add a bit more information:
There are two commonly-used schemes to write plugins for Web browsers: NPAPI (the plugin scheme invented by Netscape) and PPAPI (the plugin scheme invented by Google for Google Chrome). Most browsers use NPAPI.
Some versions of Chrome can use NPAPI or PPAPI plugins, but you don't want to install the same plugin twice else you risk breaking things in weird and interesting ways. Google announced a while back that they would be discontinuing support for NPAPI plugins; I don't know if the current version of Chrome can use them or not.
