There are a lot of blog posts out there telling people that they can dramatically improve Firefox's performance by making certain tweaks in about:config. It's worth saying up front that the default settings are the way they are for a reason. The Mozilla team is not secretly trying to deprive you of additional performance. A good example is pipelining, which isn't supported by all web servers. Not only is it not universally supported, but because of the architecture of this feature set, it's not possible for Firefox to only use it when it is available. That being said, if you know what you're doing and you do see a performance boost, I say go for it. Just don't complain if you experience problems as a result.
So, what promoted this post? It was Egon's post titled The Truth About the Firefox "Pipelining" Trick. That post is one of the more sane explanations I've seen in recent months and if you're interested in Firefox and pipelining, it's worth your time to read it.