Firefox 5 is a week away from being released as a final version. The browser is expected to be released as final on June 21. When you look at the changelog you will notice quite a few under the hood improvements that have not been talked about yet. HTTP Transactions sorted by CWND is one of those features. Most users probably wouldn’t associate a faster browser with that feature in particular, but the explanation on the Bugzilla site might change that.
"What really distinguishes different connections to the same server is the size of the sending congestion window (CWND) on the server. If the window is large enough to support the next response document then it can all be transferred (by definition) in 1 RTT."
It basically means that Firefox may load resources faster if connection handling and priorities are changed.
"I’ve done an experiment to show the best case – a link to a 25KB resource off of a page that contains a mixture of small and large content. In both cases the 25KB resource is loaded with an idle persistent connection. In the historic case it reuses a connection that had loaded a small image previously and it takes 3RTT (793ms) to transfer it.. in the case of sorting by cwnd the window is large enough to accommodate the entire resource and it is all complete in 1 RTT (363ms). Cool!"
Even better, the worst case scenario is the status quo of Firefox 4. Users who are interested in a longer, more technical explanation, can visit the Bitsup blog for a taste of that.
In other News
Firefox has a bad reputation for excessive memory usage, and related to this slow downs especially on startup or when closing the browser window. While that is certainly not the perception of all Firefox users, many perceive Firefox as a browser that uses to much memory.