How to open a url?

How do i open a url in this main menu for facebook: http://gyazo.com/1cf969a4e7d9fd0c15c0c098684e0dc5
how to fix it in this Game menu script

Code (CSharp):

1. var isQuit=false;
2.  
3. function OnMouseEnter(){
4.     //change text color
5.     renderer.material.color=Color.red;
6. }
7.  
8. function OnMouseExit(){
9.     //change text color
10.     renderer.material.color=Color.white;
11. }
12.  
13. function OnMouseUp(){
14.     //is this quit
15.     if (isQuit==true) {
16.         //quit the game
17.         Application.Quit();
18.     }
19.     else {
20.         //load level
21.         Application.LoadLevel(1);
22.     }
23.    
24. }
25.  
26. function Update(){
27.     //quit game if escape key is pressed
28.     if (Input.GetKey(KeyCode.Escape)) {
29.             Application.Quit();
30.     }
31. }

 

Application.OpenURL

 

But how do i fix it for when you click the facebook button and it will only load one page of the facebook?

 

Place it somewhere where it will only be called once, such as the OnMouseUp function.