dont be so sure that the key is fake
in the past 6 months, there has been a glut of those counterfeit messages, apparently because MS just decided to block a block of keys, legit or not.
my key is legit and I was one of the blocked ones.
once you get an update installed, cant remember which one, it gives off the counterfeit message.
call MS using the activation number and speak to an operator before you do anything else.
https://www.google.ca/search?q=windo...irefox-nightly