Netlib is the fond name of the original networking library that has been with us since Navigator 1.0. Here are some documents that describe how it works:

Netlib, from the top

Core Functionality

http1.1 version compliance chart

Cache FAQ

Under the Covers

Misc

netlib diagrams and docs by Thierry Bezecourt
File index
Initialization
Cleanup

netlib II

Written in the 4.0 Navigator/Communicator timeframe and ultimately shipped with some server products. It was written in C using this wonderful tool called JMC (the Java Module Compiler) that predates our use of COM and C++. Here are some fun documents about it if you can't sleep:

janet

Java-based networking library developed for the Xena project. The code may be getting published on mozilla.org one of these days...

bam

The BAM (Born-Again Modularity) effort was started in conjunction with the New Layout project (aka Gecko) in order to fit the new layout engine into the old codebase (now Mozilla Classic). Part of this was COMifying netlib, giving it a reasonable XP-COM veneer while all sort of horrors remained lurcking beneath the surface, ripe for a rewrite. Here's some info:

March, 1998 - BAM netlib remodularization doc

n2

Earlier attempt to rewrite netlib for Seamonkey. Here are a few pointers:

Kickoff meeting notes
The Netlib Micro Kernel - Chrisf
Raman's draft on the new architecture with Mail/News perspective

necko

Here we are today, trying to replace netlib once again. The Nth time's a charm.