Just another quick collection of my findings on the internet. For the moment until IPv6 becomes far more widespread it's typically best to disable it to avoid complications. For more details regarding the Pipelining settings, see http://egonitron.com/2007/05/25/the-truth-about-the-firefox-pipelining-trick/
Within Firefox on Ubuntu 10.04, I use the following settings (in your URL bar, goto about:config)
Set network.http.pipelining TRUE Set network.http.pipelining.maxrequests 8 Set network.http.proxy.pipelining TRUE Set network.dns.disableIPv6 TRUE
Disabling IPv6 stops FireFox wasting time trying to resolve to an address you're never going to connect through because (at this stage) your ISP doesn't support it.