It was deprecated for a long while. And has been removed since 1.9.
To still be able to use the $.browser you should add the following JS, or visit the project on github:
<script src="http://code.jquery.com/jquery-migrate-1.0.0.js"></script>
See the version 1.9 changelog:
http://blog.jquery.com/2013/01/15/jquery-1-9-final-jquery-2-0-beta-migrate-final-released/
More info on upgrading
http://jquery.com/upgrade-guide/1.9/
