I've been combing through a World War II Encyclopedia. What I find interesting is there are a lot of pics of Shermans without the .50 cal. It makes me wonder if they were often removed?
There is one picture of three Shermans taken from perhaps six stories up. The caption reads "American Firefly tanks roll through a Normandy town." Although I thought the Firefly was purely a British variant, the gun looks long enough to be a 17 lbr and the turret looks to have the same counterweight. At any rate, they appear to have pintle mounted MGs, although admittedly due to the distance it is hard to be certain if the small lines are in fact an MG or some other aparatus.
In another volume it lists the "American/British Sherman M4A4/VC Firefly Tank" and gives some specs including a "one .5-inch Browning machine gun".
Not sure that adds anything to the discussion . . .