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If you want to go Flashless on Mac and Safari, it's possible to use Firefox as a fallback, too, not just Chrome. While Firefox does load Plugins from /Library/Internet Plug-Ins and ~/Library/Internet Plug-Ins, it looks in other places too. I just tested and it seems to work fine from ~/Library/Application Support/Firefox/Profiles/<profile name>/plugins and I suspect /Applications/Firefox.app/Contents/MacOS/plugins would work too.

So you can copy Flash Player.plugin, NP-PPC-Dir-Shockwave and flashplayer.xpt to one of the Firefox specific folders and launch Firefox from Safari's Developer menu. Chrome starts up faster, though.