Folks who do Actionscript 3 development on a daily basis probably know this. Probably everybody knows this except me. There is a debug version of the Adobe Flash Player:

http://www.adobe.com/support/flashplayer/downloads.html

It can be configured like so:

http://kb2.adobe.com/cps/403/kb403009.html

Also note that the debug version will not be used within Google’s Chrome.