flash code causes url to open twice

//import the flash filter classes that also included the GLOW filter
import flash.filters.*;
//import the tween classes to give a little bouncy effect to object 
import mx.transitions.Tween;
import mx.transitions.easing.*;
 //ok instead of putting those parameters directly into the GlowFilter Object
// I've assigned those parameters to variables for ease of change and understand
var glowColor:Number = 0xFFFF00;//color that will glow around the object
var glowAlpha:Number = 25;// transparancy of the color
var blurX:Number = 10; //initial value of color floodingin horizontal direction
var blurY:Number = 10; //initial value of color floodingin vertical direction
var glowStrength:Number = 3; // the more the value the more the strength of the glowcolor
var glowQuality:Number = 3; // qulaity of the glow, it is set to max now
var glowInner:Boolean = false; // unable inner glow 
var glowOuter:Boolean = false; // unable outer glow 
//all the Glow properties mentioned in the GlowFilter are assing to the variables
var glowMe:GlowFilter = new GlowFilter(glowColor, glowAlpha, blurX, blurY, glowStrength, glowQuality, glowInner, glowOuter);
// GlowFilter properties has given to the Object
btn_mc.filters = [glowMe];
//function for the RollOver event with dynamic Glow setting.Glow setting changes on RollOver
btn_mc.onRollOver = function() {
	growBall();
	this.onEnterFrame = function() {
		if (glowMe.blurX<40) {
			glowMe.blurX += 2;
			glowMe.blurY = glowMe.blurX;
		}		
		else {
			delete this.onEnterFrame;
		}
		this.filters = [glowMe];
	};
};
//function for the RollOut event that takes back the object glow to its initial stage
btn_mc.onRollOut = function() {
	shrinkBall();
	this.onEnterFrame = function() {
		this.filters = [glowMe];
		if (glowMe.blurX>10) {
			glowMe.blurX -= 2;
			glowMe.blurY = glowMe.blurX;
		} else {
			delete this.onEnterFrame;
		}
	};
};
btn_mc.onPress = function ()
{
   getURL("http://www.tomahawktko.com", "_self");
}
 
// button GROW and SHRINK code starts here
var xGrow:Tween;
var yGrow:Tween;
var xShrink:Tween;
var yShrink:Tween;
 
btn_mc._xscale = btn_mc._yscale = 50;
 
function growBall(){
    xShrink.stop();
    yShrink.stop();
    xGrow = new Tween(btn_mc, "_xscale", Elastic.easeOut, 50, 58, 2, true);
    yGrow = new Tween(btn_mc, "_yscale", Elastic.easeOut, 50, 58, 2, true);
	
}
function shrinkBall(){
    xGrow.stop();
    yGrow.stop();
    xShrink = new Tween(btn_mc, "_xscale", Elastic.easeOut, 58, 50, 3, true);
    yShrink = new Tween(btn_mc, "_yscale",Elastic.easeOut, 58, 50, 3, true);
}
 
 
 
/*
function doTween() {
	var mcXScale:Tween = new Tween(btn_mc, "_xscale", Elastic.easeOut, 100, 40, 3, true);
	var mcYScale:Tween = new Tween(btn_mc, "_yscale", Elastic.easeOut, 100, 40, 3, true);
} */

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