How to open a url?

Unity Engine
1

How do i open a url in this main menu for facebook: Screenshot - 1cf969a4e7d9fd0c15c0c098684e0dc5 - Gyazo
how to fix it in this Game menu script

var isQuit=false;

function OnMouseEnter(){
    //change text color
    renderer.material.color=Color.red;
}

function OnMouseExit(){
    //change text color
    renderer.material.color=Color.white;
}

function OnMouseUp(){
    //is this quit
    if (isQuit==true) {
        //quit the game
        Application.Quit();
    }
    else {
        //load level
        Application.LoadLevel(1);
    }
   
}

function Update(){
    //quit game if escape key is pressed
    if (Input.GetKey(KeyCode.Escape)) {
            Application.Quit();
    }
}
2

Application.OpenURL

3

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

4

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