Scott Mitchell wrote a post about performance using Cassini (the "integrated" Development Server in ASP.NET) when running sites under Firefox. Having myself been living with this issue for a long time, but just blamed my dev setup, this news is sweet music in my ears.
Just did the "network.dns.ipv4OnlyDomains" fix (i.e. about:config -> set network.dns.ipv4OnlyDomains to "localhost") and everything seems like I just received the latest state-of-the-art dev machine (well almost ).
Therefor if you have not done it already, what are you waiting for go right ahead! Just type about:config in your location bar.