Very slow downloads in the "download manager"
Hello! Very slow downloads in the "download manager"(Ctrl+J). Download speed does not exceed 500Kb/sec. Sometimes the speed shows more only at the initial stage of loading, then it drops to 500. The speed of my internet connection is "1 Gigabit". I do not experience speed problems if I use third-party download managers, for example "Download Master"(westbyte.com). Why such a low speed in the built-in download manager of the Mozilla Firefox browser? One file is loaded or several simultaneously at all the speed is not more than 500Kb this is a disaster. What can I do to make the built-in boot manager work at full strength and not limit the download speed?
Windows 7 Ultimate (x64), Firefox 53.0 (32 bit)
Regards,