Fiddler - Fiddler is a debugging program for websites.
Fluxguard - Deployment, Defacement, & Security Monitoring
Firefox JavaScript Debugger - Firefox JavaScript Debugger is a rich-functional website monitoring tool that provides you an opportunity to step through JavaScript code and test or modify its state, helping in tracing the bugs from all over the network.
Inspect Element - Inspect Element is a multi-functional tool that is introduced to get information about what makes the web tick, figure out what is broken in your sites, and mock-up what a specific color or font change would look like.