Extra waterfall element unused connection

Modern browsers spin up multiple connections with a web server to retrieve the elements of a web page as fast as possible. They do this because creating each connection takes time, especially when HTTPS is involved. Some of these connections are kept open for a while before an actual HTTP request is sent across that connection.

This extra “unused” time wasn’t displayed in waterfalls until now. Starting with Firefox FPCs, we’re going to display that these connections are created early and only get used later on in the timeline. We’re showing this extra timing aspect using a new element in the waterfall: unused connection.

Introducing this element will give a more accurate representation of what actually happened in the browser. It will reveal that different browsers handle multiple connections in different ways.

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