From MozillaZine Knowledge Base
HTTP is the application-layer protocol that most web pages are transferred with. In HTTP 1.1, multiple requests can be sent before any responses are received. This is known as pipelining. Pipelining reduces network load and can reduce page loading times over high-latency connections, but not all servers support it. Some servers may even behave incorrectly if they receive pipelined requests. If a proxy server is configured, this preference controls whether to attempt to use pipelining with the proxy server.
Possible values and their effects
Attempt to use pipelining in HTTP 1.1 connections to the proxy server.
Never use pipelining. (Default)
Users who want better page loading speed can try setting this preference to true, keeping in mind this may break some websites.
First checked in
Has an effect in