Have you tried another browser? It may not be firefox error
Works fine for me in the current release.
It looks that this done via a websocket (wss://stream.binance.com/stream) if I check this in the Web Console and Network Monitor.
You can check the Web Console for websocket related messages.
You cant try to toggle this pref on the about:config page to see if true or false makes a difference (both work for me).
You can also check other websocket pref to see if they are all default.
network.websocket.timeout.open = 100 :)