Backup CDN Javascript Library Location

Our web app uses开发者_如何学C the Google CDN to link to the jQuery library and it's starting to become very prevalent on our site. We have a major problem every now and then when clients install a firewall and specifically allow our website - but they know nothing of these external javascript libraries. It's not a simple case of doing something like checking whether the client can run Javscript - because they can ... they just don't get jQuery and hence functionality is broken.

Is there such a thing as a "backup" JS library where I can specify two locations to check? My other alternative is to provide an FAQ entry for people using a firewall. Hosting the libraries locally isn't really a good idea for us because we're trying to keep bandwidth down, and I like having those libraries elsewhere.

If I include two <script> tags it will download them both, correct?

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<script>!window.jQuery && document.write(unescape('%3Cscript src="js/libs/jquery-1.4.2.js"%3E%3C/script%3E'))</script>

Found here Fallback for jQuery UI from google CDN