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.
Many problems with pipelining are related to broken proxy servers sitting between the user and the destination web site. Since this is not a problem with SSL, it is possible to turn on pipelining for SSL websites only. This preference controls whether to use pipelining for secure websites, regardless of network.http.pipelining.
Possible values and their effects
Use HTTP pipelining for secure websites
Do not use HTTP pipelining for secure websites, unless network.http.pipelining is true (Default)
First checked in
Has an effect in