I think the "problem" is in safari and webgl.. Maybe i get lower fps because i run my game with the safari under windows..
I search in google for safari and webgl and i find this:
-In Safari, open the Safari menu and select Preferences.
-Then, click the Advanced tab in the Preferences window.
-Then, at the bottom of the window, check the Show Develop menu in menu bar checkbox.
-Then, open the Develop menu in the menu bar and select Enable WebGL.
Maybe in next update for safari in windows.. have this option! : -)