Nosniff header support coming to Chrome and Firefox

That is similar to what github pages is. The limitation is just that the file must be in github pages and you can only get to the current file in the gh-pages branch.

https://raw.github.com/documentcloud/underscore/master/under...

won't work but

http://documentcloud.github.io/underscore/underscore-min.js

will.

Also it looks like there is already a workaround to get to raw pages: https://rawgithub.com/

There are a couple of ways that it can be worked around for jsfiddle (assuming you use the "External Resources" tab). One is to pull the file in through an AJAX request and then eval the result. The other is for the backend to pull the script and serve it with headers stripped. The latter approach would be preferable, because then they can use a reasonable caching strategy and not drain github's resources.

It would, but it would create other problems also. If I were to link to a raw.github.com URL on HN, it would be disallowed because the Referer header would be "incorrect".