I have run several tests on the web site of the German Solar Industry Association - and the results are consistently only "F"s (something I have never ever seen before in webpage test): http://www.webpagetest.org/result/151008_VG_14W1/
The one thing that absolutely really puzzles me: None of the static resources comes with a max-age or expires header. And still: They are not downloaded in the repeat view. In repeat view, only the HTML page itself and the Piwik statistic script is called (requests go down from 55 to 2, Bytes from 1,051 KB to 35kB).
How is this possible? Why don’t the browsers (I tested FF and Chrome) try to download the static assets, again? What caching mechanism is used here?
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OK, I found out, why the browsers do not re-download static assets: Using LiveHTTPHeaders on my local FF, I can see that in fact there are expires headers sent. The time is short (just one week), but it is enough to no re-download the assets.
The strange thing is: If I look at the http response given in WPT, no expires headers show up. They seemed to be stripped from the reply of the server. The browsers use them nevertheless.
Is this a bug in WPT? I tested two different instances with the same result…?