How do I make Firefox use Chrome's built-in Flash plugin?
Chrome keeps the plugin in:

/Applications/Google Chrome.app/Contents/Versions/{current_version}/Google Chrome Framework.framework/Internet Plug-Ins/Flash Player Plugin for Chrome.plugin/Contents/MacOS/


For me current_version is 16.0.912.63

Firefox uses Adobe mainstream version of Flash player, which is installed in:

/Library/Internet Plug-Ins/Flash Player.plugin/Contents/PlugIns/FlashPlayer-10.6.plugin/Contents/MacOS


The size difference is quite big (35MB mainstream against 16MB Chrome version). I actually tried to make such trick by making symbolic link to chrome version in place of mainstream version, but Firefox didn't like that (did not show any content where flash should be). 

Looks like it's not that simple as it is in Linux.

EDIT:

It turns out that it actually is that simple:


  Copy Chrome's Flash plugin,


/Applications/Google Chrome.app/Contents/Versions/16.0.912.63/Google Chrome Framework.framework/Internet Plug-Ins/Flash Player Plugin for Chrome.plugin



  to 


/Library/Internet Plug-Ins/Flash Player Plugin for Chrome.plugin



  and they both work.