Here it is (edited it a little):
Open your Firefox browser and type about:config on the address bar. Select the following lines and double click to toggle or change value. You can filter to find the lines faster.
These must be the value for better performance of your Firefox:
- network.http.pipelining: True
- network.http.pipelining.maxrequests: 10
- network.http.proxy.pipelining: True
- network.dns.disableIPv6: True