Hello,
Actually, I have a little problem, it seem this problem appear after the last Nethserver update, But i’m not certain::
When I go for the first time on a site, this one seem take a very long time to show up in the browser… The page still blank.
But, when I interrupt the load and click on the refresh bottom … The page show up rapidly.
It seem a problem with the proxy, but I don’t see nothing abnormal in the log…
Where to search?
Is it only that site? which site is it?
No… All sites that aren’t yet in the cache… And I flush the cache.
I have no problem at all. It’s works fine and fast.
Could it be a problem with your browser?
I flush the cache in the browser too,
but I don’t see any enhancement… 
How to see if it’s the provider? Which tool I can use? ntop?
From the command line try a ping to the page (e.g ping google.com). A ping to a page in Australia needs around 30ms, because I am in Australia, and to Germany around 410ms. If the page hosted in your country and it needs longer than is something wrong.
You can check your internet speed with http://speedof.me/. It’s works without flash so you don’t need any insecure addons. It will download from small to large size files and you will see in the graph how the current download speed is. Also it test your upload speed as well.
check /etc/resolv.conf and see if it has the proper DNS servers. Perhaps the wrong ones are listed which could be causing a delay in resolving names.
I will check this, now that you said, this week I had to reboot the internet router modem…
I will observe few days, but it seem you are right, the Nethserver point on Open Dns, when the Isp dns point on Google Dns
I return in few day to confirm… Thank you @islipfd19
And since a time, I want to configure it as bridge only, and let Nethserver do the Pppoe connection… I will do this this week