For those who complain about the slowness, there is a way to tweak a setting in firefox so that the game has a normal speed.
To do this, you need to type in the address bar: about:config
then in the search bar you type:
network.http.max-connections-per-server new numeric value: 10
I also modified: network.http.max-persistent-connections-per-server and set the value to 10.
you restart the browser and it's done
don't hesitate to give your feedback afterwards