It's interesting to see the impact that having the developer tools open has on performance, and whether the network tab is being shown or not. While HTTP2 is generally faster for me, opening the developer tools makes both significantly slower, and seems to have a larger impact on HTTP2, usually making it slower than 1.1, in both Firefox and Chrome.
Developer tools internally proxies every request. The proxy interface it uses is a custom devtools protocol, and can't handle every part of http - for example, at assumes all post request bodies are delivered in one go rather than streamed.
It also uses the same single JavaScript thread to proxy the requests as is used for rendering the devtools UI, which can't be great for performance.
