I don't mean to rain on your parade, SS... but I've seen this posted on a number of forums now, and I'm a little concerned about the flow-on effects of this tweaking of Firefox.
It works by increasing the number of simultaneous connections made to a Web server to download a page, in much the same way download accelerators like Getright make multiple connections to a server to download more chunks of a file simultaneously. This is great for the user, but not so wonderful for the server.
As more people take these tweaks on board, especially in communities such as this, the servers will start being hammered more and more, and one or both of two things will happen: the effectiveness of the tweak will diminish, because there's only so much bandwidth to go around, and it may have unpredictable effects on the less stable Web servers out there. As more people are hammering servers, and taking all the bandwidth, more people will miss out and not enjoy the same quality of service from a particular server.
I can also see that changes will be made by Webmasters very soon to strictly limit the number of simultaneous connections per IP. My advice, not so much from a technical standpoint as from an ethical, would be to not modify Firefox's settings unless you are experiencing service degradation (in comparison with say IE.)