Within Typekit’s ‘Help’ section:
Q: Fonts aren’t displaying or look “doubled” in Safari & Mobile Safari
A: The font weight or style in the CSS isn’t available in the kit. If the specified font weight or style isn’t included in your kit, these browsers may try to create it. Make sure that the weight and style you want to apply are included in your kit and that they are specified correctly in the CSS.
I know it’s not the correct browser issue… but sometimes they just render differently– even if you don’t declare a weight in your CSS