A page refresh would usually take up to 3 seconds (localhost) even without changing the source code (so it should be instantaneously, especially now that I’m using a SSD).

It appears that there is some kind of bug on Vista/Windows 7 with DSN and IPv6, but that can be easily fixed. Here are some of the solutions I have found:

1. Recommended Solution – machine wide: uncomment the localhost address in the hosts file (%WINDIR%\System32\drivers\etc\hosts): (source)

# localhost name resolution is handled within DNS itself.

127.0.0.1       localhost

# ::1             localhost

# localhost name resolution is handled within DNS itself.

127.0.0.1       localhost

# ::1             localhost

2. Firefox-only solution: disable IPv6

1. Type about:config in the address bar and press Enter.

2. Scroll down until you find network.dns.disableIPv6.

3. Double-click on it to change its value to true.

4. Restart Firefox.

3. System wide-configuration (option 1): Disable IPv6 Random identifier

netsh interface tcp set global autotuninglevel=disabled

4. System wide-configuration (option 2): Disable IPv6 from Your LAN Interfaces and Connections

1. Launch Vista, click on Start, and then click on Run. Once the Run window appears, type regedit.

2. Once you have accessed the registry, you will add a registry value as follows: (DWORD type) Set to OxFF.

3. The registry is as follows: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\DisabledComponents