Forcing firefox to keep a connection alive for reuse

[Michael_google gmail_Gersten]

(slightly off topic)

I was just realizing that the overhead of making dozens of separate
connections for fetching everything off the web (one connection per
item) instead of reusing the same connection to the server is probably
part of why browsing through tor is as slow as it is.

How do you force firefox to "keepalive" the connections?

(I can't be the first person to think of this, so either (A) it's
hard, or (B) my system is somehow misconfigured.)