Upon further reading I have found the following.
It does not work in NN6.0/6.1
It will work in NN6.2 and above and Mozilla 0.9.2 and higher, but only if you follow the instructions here
This isnt for the faint hearted though as it involves dipping into editing mozilla's and the pluggins code and compiling them using an XPCOM compatibale compiler.
Communication between the browser and Flash is much more robust and reliable using a third party script I'd say.