A new flag (e.g. "reversed") could be added to $.Callbacks object, which would make callbacks.fire() method to fire callbacks in reversed order.

Stack-based execution patterns are very popular and this flag would add another possible usage to this simple yet powerful tool.

Example:

function fn1( value ) {
  console.log( value );
}
function fn2( value ) {
  console.log( "fn2 says: " + value );
  return false;
}

var callbacks = $.Callbacks( "reversed" );
callbacks.add( fn1 );
// Outputs: foo!
callbacks.fire( "foo!" );
callbacks.add( fn2 );
// Outputs: fn2 says: bar!, foo!
callbacks.fire( "bar!" );