// Correct location for this function
function motocidTinyBump() {
  var tmp = $('table.mceEditor'); // Saved for performance, $('...') is an expensive operation
  tmp.attr('width','100%');
  tmp.attr('style','');
  tmp = tmp.Find('iframe'); // Get 'iframe' inside of 'table.mceEditor', could theoretically be faster, not sure if it is or if it really works like this. Try it out.
  tmp.attr('width','100%');
  tmp.attr('style','');
}

if (Drupal.jsEnabled) {
  $(document).ready(function(){
    $('#node-form .jstabs a').click( motocidTinyBump ); // Removed ()
  });
}