creo que buscas algo así...
Código HTML:
Ver original<script type="text/javascript"> function MostrarContenido(id){
var Contenido = document.getElementById(id);
if(Contenido.style.display == 'none'){
Contenido.style.display = '';
}
else{
Contenido.style.display = 'none';
}
}
<li onclick="MostrarContenido('Cont1');">Contenido 1
</li> <li onclick="MostrarContenido('Cont2');">Contenido 2
</li> <li onclick="MostrarContenido('Cont3');">Contenido 3
</li>
<div id="Cont1" style="display:none;"><h2>Cont 1
</h2> Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s
<div id="Cont2" style="display:none;"><h2>Cont 2
</h2> Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s
<div id="Cont3" style="display:none;"><h2>Cont 3
</h2> Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s
prueba haber si te sirve
Nota: las ID no deben de repetirse dentro del mismo HTML, por como veo tu html estas repitiendo la id mostrarDiv y flotante