How to get Fiddler to work under Windows 7

If you try to trace your web applications using Fiddler with default settings under Windows 7, you will get the following error in your browser:

[Fiddler] Connection to localhost. failed.
Exception Text: No connection could be made because the target machine actively refused it ::1:80

This can be fixed by disabling IPv6 in Fiddler:

1. Go to Fiddler, then Tools > Fiddler Options.
2. Uncheck "Enable IPv6 (if available)".

Tracing should now work.