because there are right now no plugins availible for Fusion8 (older ones wont load) and there where never a OSX version of it before the help you will get here is limited. but maybe soemon from BMD can say something about it.
also, right now it seems that even OFX plugins wont work in the current beta, but these plugins need to be installed "normal" (as provided by the plugin). they will be installed in a commom OFX plugin folder, so every application which can run OFX can find them.
but if your in Fusion go to the preferences and take a look at the "path map" section, there is an entry for plugins if you hit the "folder" icon to change the path it should default open the directory it has currently in use