"Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP(S) traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler includes a powerful event-based scripting subsystem, and can be extended using any .NET language. Fiddler is freeware and can debug traffic from virtually any application, including Internet Explorer, Mozilla Firefox, Opera and thousands more."

This is the official change log:

This is the official change log:
- Improved support for Windows Phone emulator.
- Edit preferences with about:config.
- Many bugfixes.
This update fixes a lot of bugs and has various smaller improvements. The change log can be found here.
Download Fiddler v2.3.1.0 (Fiddler2Setup.exe) here.
Download Fiddler v2.3.1.0 (Fiddler2Setup.exe) here.