Firefox ESR became very slow with a network profile

Question

We are using Firefox (on Windows) in our company with network based profiles on a local server. It worked fine until Firefox ESR 52.3. But then we switched to ESR 52.4 and later 52.5. Now the access to any website is very slow. So if I call a website (even in the intranet) it can take about 60 to 180 seconds until the website opens. If I call the site meanwhile in Vivaldi or Internet Explorer it opens immediantely. Using Wireshark I saw that Firefox is writing data to the network profile in many many tiny packets of 4 bytes (my logfile became 120 MB of size). It tested the same (same profile) with firefox ESR 52.3 and Firefox 57. Both write fast in large packets (i.e. 65536 bytes). Is there any chance to change the package size? The only solution so far seams to move the profile to the local disk. But if I do so, it is no longer part of the server backup.