piroJOKE wrote:But how is it that in FF it works fine, bun in PM need «some magic»?

Pale Moon is not Firefox.
And why Steam doesn't want to send us everything on the first go is a good question. There's no real way for us to know why it gets hung up on their end. If you have time to experiment, then you can try and see if disabling HTTP pipelining (controlled by network.http.pipelining and network.http.pipelining.ssl) will help. If it does, then something on Steam's end (possibly a load balancer or reverse proxy) doesn't understand this part of the HTTP 1.1 standard very well and may need to be looked at by them.
Set both preferences to false and restart the browser.
I looked at SPDY as well as a possible culprit but I have that disabled myself by default, so that can't really be it if you have it on default settings.
"Son, in life you do not fight battles because you expect to win, you fight them merely because they need to be fought." --
Snagglepuss
