It depends, but the way this particular combination works is...
Firewind Blade's property inherently goes off when the weapon is used in an attack that hits.
Blazing Arc Ki focus' item power is an at-will free action when you make a melee attack.
An attack with a weapon substituting a ki focus' power is legit, because both instances of triggers are being met.
--
Accel R8
(This space for rent)!