Jiffy is an end-to-end real-world web page instrumentation and measurement suite.

Have you ever been interested in what extensions are available for Firebug?

JOrtho (Java Orthography) is a Open Source spell-checker entirely written in Java. Its dictionaries are based on the free Wiktionary project and can therefore be updated by virtually any language.

jGrowl is a jQuery plugin that raises unobtrusive messages within the browser, similar to the way that OS X’s Growl Framework works.