Rated 3 out of 5 stars
first, regarding those comments about venkman being difficult to learn: the help files are reference documents, not tutorials. to learn how to use venkman, google "venkman tutorial". the first one listed got me up and running venkman quickly without problem.
second, as soon as i tried to "stop" scripts with venkman, i had trouble with firefox freezing until i clicked continue with venkman. i uninstalled firebug and restarted ff but the problem persisted.
i have other debugging plug-ins including flashtracer and web developer that may be part or all the problem but i wasn't willing to uninstall those even if venkman would work well afterwards.