window.onload = function() {
  document.onselectstart = function() {return false;} // ie
  document.onmousedown = function() {return false;} // mozilla
  document.oncontextmenu = function() {return false;} // for images
}

window.onload = function() {
  var element = document.getElementById('content');
  element.onselectstart = function () { return false; } // ie
  element.onmousedown = function () { return false; } // mozilla
  element.oncontextmenu = function() {return false;} // for images
}