Fixed with Firefox Version 3.0.9. I don't know if is something specifically related to the browser but yesterday it downloaded the new version and installed, and problem solved. The data is actually what i sended plus the js code:
$.ajax({ type: 'POST', url: 'file.php', dataType: 'json', success: function(mensaje){ alert(dump(mensaje)); }, }); I use this for dump (maybe helps someone). http://www.openjs.com/scripts/others/dump_function_php_print_r.php Thanks, I will use try again with a not updated firefox again and see what's going on.