nsITimelineService in Firefox 3.0

 nsITimelineService is used to constuct a timeline of program
 execution.  The timeline is output to a file, either stderr or the
 value of the environment variable NS_TIMELINE_LOG_FILE.  On the
 Mac, the timeline is output to the file named "timeline.txt".  The
 reason it's different on the Mac is that the Mac environment
 initialization code happens after timeline initialization code.
 
 If NS_TIMELINE_INIT_TIME is set in the environment, that will be
 used as the time of startup; otherwise the current time when mark()
 is first called will be used.
 
 mark() is used to put marks on the timeline.
 
 indent() and outdent() are used to format the timeline a bit to
 show nesting.  This doesn't produce perfect results in the face of
 asychrony and multiple threads.
 
 enter() and leave() are convenience functions that add marks to the
 timeline and do indentation.
 
 startTimer() and stopTimer() control named stop watches.  If
 startTimer() is called more than once, an equal number of
 stopTimer() calls are needed to actually stop the timer.  This
 makes these timers slightly useful in a threaded environment.
 
 markTimer() puts a mark on the timeline containing the total for
 the named timer.
 
 Don't use nsITimelineService in C++ code; use the NS_TIMELINE
 macros instead.  nsITimelineService exists so that JavaScript code
 can mark the timeline.