Rob Campbell gives a neat way to debug without being specific to one type of debugging tool.
A better way is to test for each function you want to use:
if ("console" in window && "time" in window.console) // define your method
\ This has the benefit of not coding for one particular type of debugging tool, will allow for graceful fallback in the event that your feature is not defined and allow you to tailor your debugging around different feature sets.
update 2010-11-30: Rui Nibau is using another method.