The way the four fetchers are implemented is sketchy at best.
First of all three out of four (all but the favicon fetcher) try to pass for a Safari browser that they clearly are not — just drop the fake Safari User-Agent, please.
Then there is no indication of which version the request is coming from (since the sources are published different users might be using different instances with different versions, please find a way to indicate a version or a git revision, so that we can tell where the request is coming from).
Further problems are “details” of the HTTP implementation(s) used by the fetchers. A more detailed analysis is present on my blog posting at http://blog.flameeyes.eu/7hdbKe — including the reasoning of why I’m bothered by this.