http://logdigger.com/
LogDigger provides Java web application developers with instant access to application log messages directly from Firefox.
LogDigger is an extension for Firefox and Firebug that collects Log4j log messages related to requested application URL and shows them in Firebug. It’s ideal for monitoring of application log messages in cases when multiple users access the application as each user receives only events generated by his/her request.
LogDigger 0.4 is FREE for both personal and commercial use.