ipython/nbviewer — pull request #206 by takluyver (2014-02-28 22:56:55+00:00)
Title: Use the download attribute for the download notebook button

This makes the browser more likely to download the notebook instead of viewing its content, e.g. from raw.github.com

Unfortunately, this only works in Chrome, because Firefox doesn't let you force a cross-domain link to download (to be fair, that's what the spec says).