This won't work, at least on Chrome. It blocks all cross-domain requests to localhost[1]. Even if the target is used with a domain that resolves to 127.0.0.1, or has CORS completely disabled with "Access-Control-Allow-Origin: *".
[1] https://code.google.com/p/chromium/issues/detail?id=67743
I suppose it would be possible to craft a url that attacks local web services sometimes found on developer machines. If someone can confirm this is indeed the case, I'll submit a pull request to their README.