Applet asks for main method when executing, but does not have this method

I packed the project in a jar that is an applet and I want this applet to run here in the linux old firefox browser, however, it asks to select a main method, but the applet has no main method. How to make it run?

packagexxx;importjava.applet.Applet;importjava.awt.event.ActionListener;importjava.awt.event.ActionEvent;importjava.awt.Button;importjava.awt.Graphics;//importnetscape.javascript.JSObject;publicclassTesteAppletextendsApplet{publicStringconteudo="";
    public String formulario;
    public String campo;
    //public JSObject campoDoFormularioHTML; 
//
    public void init() {
          formulario = getParameter("formulario");
          campo = getParameter("campo"); 

          ActionListener trataEventos = new ActionListener(){


           public void actionPerformed(java.awt.event.ActionEvent e){
           conteudo += e.getActionCommand();
          // campoDoFormularioHTML.setMember("value", "" + conteudo);
           }

       };

       Button b7 = new Button("7");
       this.add(b7);
       b7.addActionListener(trataEventos);

       System.out.println();

       Button b8 = new Button("8");
       this.add(b8);
       b8.addActionListener(trataEventos);

       Button b9 = new Button("9");
       this.add(b9);
       b9.addActionListener(trataEventos);

       Button b4 = new Button("4");
       this.add(b4);
       b4.addActionListener(trataEventos);

       Button b5 = new Button("5");
       this.add(b5);
       b5.addActionListener(trataEventos);

       Button b6 = new Button("6");
       this.add(b6);
       b6.addActionListener(trataEventos);


       Button b1 = new Button("1");
       this.add(b1);
       b1.addActionListener(trataEventos);

       Button b2 = new Button("2");
       this.add(b2);
       b2.addActionListener(trataEventos);

       Button b3 = new Button("3");
       add(b3);
       b3.addActionListener(trataEventos);

       Button b0 = new Button("0");
       this.add(b0);
       b0.addActionListener(trataEventos);

       Button limpa = new Button("Limpa");
       this.add(limpa);
       limpa = new Button();
          // limpa.addActionListener(new ActionListener() {
    //      
//      public void actionPerformed(java.awt.event.ActionEvent e) {
//          conteudo = "";
//          campoDoFormularioHTML.setMember("VALUE", conteudo);
//      }
//     });
//              
//     JSObject objWin = JSObject.getWindow(this);
//     JSObject objDoc = (JSObject) objWin.getMember("document");
//     JSObject objForms = (JSObject) objDoc.getMember("forms");
//     JSObject objForm = (JSObject) objForms.getMember("formulario");
//     JSObject  objElements = (JSObject) objForms.getMember("elements");
//     campoDoFormularioHTML = (JSObject) objElements.getMember(campo);
//     campoDoFormularioHTML.setMember("value", ""); 
    }
}