Strange wordpress GET request

I've just upgraded to Wordpress 4.8 and in the waterfall overview I see something strange. It's a get request which is being called on any page of my website. It looks like this:

http://www.my-website-url.com/page/2 (SEE BOLD STUFF)
it's 0kb but is adds a loadingtime of 400ms.
Response headers:

Any Idea what is going on here?

Solution

The X-Moz: prefetch header indicates that this is Firefox prefetching the next page. Your software of choice probably has a <link> element or similar that indicates content that the browser might want to prefetch for faster loading if the user decides to navigate there. It shouldn't cause any delay in displaying the initial page as prefetching is only done after the page itself has finished loading. Also, I don't know where the 0Kb came from as the Content-Length header states it's about 10kB big.

For more information about Firefox's implementation of link prefetching, see:

https://developer.mozilla.org/en-US/docs/Web/HTTP/Link_prefetching_FAQ