Quantum mechanics introduces fundamental uncertainty to the equation, but it is unlikely that free will has anything to do with that uncertainty even though it does destroy predestination. While random events that occur on the quantum level result in all kinds of uncertain outcomes that affect the macro level and our decisions probably have randomness introduced to them from quantum mechanics, that doesn't mean that we make decisions in a way that has room for the concept of free will.
I'd argue that free will is an incoherent concept in the way that it's typically formulated. Think about the things that it could be...
Is free will the ability to make a decision? Nope, computers and logic flow charts make decisions. A decision is simply a mechanism wherein an action is performed on the basis of conditions. If X > Y, take action A. If Y > X, take action B. This is a logical decision point that introduces no element of free will.
Free will is some postulated extra-logical component to a decision. I suppose you could axiomatically decide that quantum randomness fits this definition, but I cannot see that as anything but arbitrary given that we have no control over it. Control seems to be key to the definition, and we certainly have the illusion of control when we engage in deliberative decision making.
It seems more likely to me that "free will" is actually a sensation, not an element of decision making. It is the realization, as a sentient being, that you've come to a decision point and must choose an outcome. That sensation sparks the process of actively combing through available data (relevant memories, active perceptions of the situation, et cetera) to generate priors to use in your decision computation. It also imbues in us a sense of sober responsibility and control over the outcome.
As evolved beings, there's an obvious evolutionary advantage to having such a mechanism. If you don't feel in control and responsible for the outcome of your actions, you won't use your higher reasoning as effectively or frequently in making decisions.
Without invoking the soul, it isn't really possible to generate an extra-logical component to decision making. I think free will's current pop-culture formulation is an old religious artifact.