In this paper, a two-period game is constructed, where duopoly firms choose advertising strategies in the first period and compete in price or quantity in the second period by maximizing the value of firm equity. Using certainty equivalence, we demonstrate the impacts of uncertainty and modes of competition on duopoly firms' optimal pricing, production, and advertising strategies. Equilibrium price and quantity outcomes emerge as significantly different from the standard industrial organization model of profit maximization. It turns out that the common measurement of market power, the Lerner index, is generally mis-stated. In contrast to the literature, we also find that firms will optimally switch from quantity to price competition either when advertising costs are low, demand is high, or if idiosyncratic risk is reduced. A series of simulations confirm these findings.