Flash Player/FireFox Different Results

Without too many details, I have a flash project that has a MOUSE_OVER function that works perfectly when I test the movie within flash and even when I play the swf in flash player. However, when open it in firefox, my mouse over doesn’t work properly. Instead of it execution the function on mouse over it executes on mouse down.

Are there any known differences between a web browser and flash player that may cause this to happen. Any help would be appreciated.