title: Javascript getting a single element on Firefox, and an array on other browsers
body: <p>So i have a form in html, with each of the options being like this: (A plethora of full pages like this can be found <a href="http://mmoviles.webs.upv.es/test_fundamentos/" rel="nofollow">here</a>)</p>
  
  <pre><code>&lt;input id="Q1opc1" name="Q1" type="radio" value="Q1opc1" /&gt; 
      &lt;label for="Q1opc1 "&gt;Froyo &lt;/label&gt; 
  
      &lt;label id="Q1extr" style="display: none"&gt;&amp;nbsp&amp;nbsp Recuerda que los nombres se asignan en orden alfabético.
  &lt;/label&gt;  &lt;/br&gt; 
  </code></pre>
  
  <p>The submit button:</p>
  
  <pre><code>    &lt;input
          onclick="comprobarRespuesta(Q1opc2,Q1,Q1extr,Q1FraseCorrecto,Q1FraseIncorrecto,Q1GrCorrecto,Q1GrIncorrecto);"
          type="button" value="Comprobar" /&gt;
  </code></pre>
  
  <p>First i pass the right answer, then the name of the radio buttons, then the id of the hints, then the id of the right and wrong phrases and images to be shown/hidden as apropiate.</p>
  
  <p>The JavaScript function looks like this:</p>
  
  <pre><code>function comprobarRespuesta(correcta, radio, extra, sicorrecto, sinocorrecto,
              iconoTick, iconoWrong) {
          var tmpChoice = radio;
          var c = radio.length;
          var correct = 0;
          for (i = 0; i &lt; c; i++) {
              if (tmpChoice[i].checked == true) {
                  extra[i].style.display = "inline";
                  if (tmpChoice[i].value == correcta.value) {
                      sicorrecto.style.display = "inline";
                      sinocorrecto.style.display = "none";
                      iconoWrong.style.visibility = "hidden";
                      iconoTick.style.visibility = "visible";
                  } else {
                      sinocorrecto.style.display = "inline";
                      sicorrecto.style.display = "none";
                      iconoWrong.style.visibility = "visible";
                      iconoTick.style.visibility = "hidden";  
                  }
              } else {
                  extra[i].style.display = "none";
              }
          }
      };
  </code></pre>
  
  <p>The problem i have is that in most browsers i have been able to test, the variable called "extra" in my function is an array of elements, so accesing extra[i] has no problems, but in firefox, extra is only the first label with that id, and not all of them, so JavaScript outputs "TypeError: extra[i] is undefined" to the console, exits, and my form behaves as it was not working at all</p>