"The correct type value for JavaScript is actually application/javascript. But wouldn’t you know it, Internet Explorer will not execute the code if you use that type value. So here’s a hell of a situation, to produce a valid HTML or XHTML document with script tags, we are required to use a type attribute, but to get it to function across all browsers we have to use an incorrect value."

SitePoint Blogs » JavaScript MIME Type: Damned if You Do, Damned if You Don’t!