Omnibug is a plugin for Firebug to ease developing web metrics implementations. Each outgoing request (sent by the browser) is checked for a pattern; if a match occurs, the URL is displayed in a Firebug panel, and decoded to show the details of the request. In addition, requests can be logged to the filesystem.
Out of the "box", it supports the following analytics providers:
Omniture, WebTrends, Google Analytics/Urchin, Google Universal Analytics, Moniforce, WebTrends, Core Metrics, AT Internet, KISSmetrics, Facebook, Torbit Insight, Quantcast, Marketo, Marketo Crowdfactory, NewRelic, Krux and Optimizely. Custom matching rules can be defined to support other systems, and support for more implementations is on the way.
Omnibug has been in use worldwide since 2007, and is now making it's debut at addons.mozilla.org