if it's being fed to a <script src=> tag, the mime should not matter. with ajax, the mime should not matter. with jQuery, it MAY matter, depending on the method used to fetch the url.
BROWSER STATS [% share]
(2013/10/31) IE7:0.5, IE8:8.6, IE9:5.3, IE10:12.3, FF:17.7, CH:41.8, SF:8.1, MOBILE:20.4