Since you are not worried about IE, why not just use css transitions to provide the animation and jQuery to change the classes. Live example: http://jsfiddle.net/tw16/JfK6N/
#someDiv{
-webkit-transition: all 0.5s ease;
-moz-transition: all 0.5s ease;
-o-transition: all 0.5s ease;
transition: all 0.5s ease;
}