The lack of a bow mounted MG is correct, the Firefly had that position removed to reduce the crew and it carried more ammunition than a regular Sherman. It did retain the coaxial .30 cal MG as a ranging machine gun, on the left of the 17 Pdr.
The British and Canadian Shermans did not deploy the turret mounted M2 .50 cal.
The Firefly would have had the option, like other British Shermans, to have a .30 Browning on the turret.
Unless somebody can provide a photo to the contrary it should be removed (the 50). Museum tanks are not proof of wartime designs.
As for having a 30 caliber...I would say it was optional, as the Brit Shermans did have them armed that way, and you must remember that a photo of a Firefly without the turret MG doesnt "prove" it wasnt installed, ALL tanks had the turret MGs removed and stored inside the tank. Placing it in the mounting was the tank commanders call. Often it wasnt deemed as needed, so it stayed unmounted. Or, moving through dense brush, or if they were expecting an enemy barrage, are all reasons to keep it unmounted. US Army Sherman photos are the same, sometimes there is no 50 mounted, simply because its not mounted on the tank at the time the photo was snapped.
Model of a Candian Firefly with a .30 mounted:
http://hsgalleries.com/images/fireflybf_1.jpgPhoto of a Firefly with a turret MG under a cover (looks like a .30 to me):
http://mailer.fsu.edu/~akirk/tanks/GreatBritain/GB-ShermanFireFly-Normandy.jpg
