Firefox “default” max download speed for xhr request

[DSDev7]

I'm developing a HTML5 app, that is downloading some large data form servers via xhr. In chrome and IE11 the data downloads pretty fast, in firefox it's much slower. I've created the simple speed check which showed me, that in firefox the download speed is about 100Mbps, and I'm testing it on 1Gpbs bandwidth.

Is there some download speed limitation in firefox? (using Firefox Developer Edition 38.9a2 on Windows Server 2012 R2, but works same on regular Firefox non-developer edition)

Thanks for all suggestions.