Not that enough people use them at the moment, but loading from random sources would mess up Content Security Policies.

* Security/Guidelines/Web Security - MozillaWiki || https://wiki.mozilla.org/Security/Guidelines/Web_Security#Co...

Mozilla makes a good tool to let you scan and report on this sort of thing for any site.

* Observatory by Mozilla :: Scan Results for news.ycombinator.com || https://observatory.mozilla.org/analyze.html?host=news.ycomb...