No, you can't add this missing pref back.
Support to disable keep-alive has been removed and keep-alive is always enabled.

See "A Preference to disable HTTP Keep-Alive has been removed":

• https://developer.mozilla.org/en-US/docs/Site_Compatibility_for_Firefox_17
• Bug 770331 – Remove HTTP Keep-Alive disable pref

since this preference has been removed is there anyway to make fire fox faster >? although this basically states that it is always enabled is there anyway to make firefox faster without touching the keep alive function.

Thank you ... for answering and being helpful

I can't get into rooms in pogo using firefox need your help 19.0 is not working right how can I get back to fire fox 18? Diana

@ Beyondsight: I assume you're referring to the wikihow pipelining tutorial. Since keep-alive's now on by default, there's no need to turn it on. Just skip that first step and do the rest, and you should get the specified results; I did.