C#

int x = 283; // X coordinate of the click
int y = 342; // Y coordinate of the click

IntPtr handle = two.Handle;
StringBuilder className = new StringBuilder(100);

while (className.ToString() != "Internet Explorer_Server") // The class control for the browser
{
    handle = GetWindow(handle, 5); // Get a handle to the child window
    GetClassName(handle, className, className.Capacity);
}

IntPtr lParam = (IntPtr)((y << 16) | x); // The coordinates

IntPtr wParam = IntPtr.Zero; // Additional parameters for the click (e.g. Ctrl)
const uint downCode = 0x201; // Left click down code
const uint upCode = 0x202; // Left click up code
SendMessage(handle, downCode, wParam, lParam); // Mouse button down
SendMessage(handle, upCode, wParam, lParam); // Mouse button up