I didn't understand why firefox suddenly is very slow while
programming and running on localhost. I've found this article
"Fixing Firefox Slowness with localhost on Vista (or XP with
I'm using Windows 7 and not Vista or XP but the solution
To make the change, type about:config in the
address bar, locate the network.dns.disableIPv6 setting
and double-click on it to set it to true.
See this URL from Dan Wahlin: