Normally when you run your application through a browser like Firefox you don't get to see Trace output like you would when previewing the app through the Flash Authoring Tool.
Someone built a firefox plugin to show Flash trace output. Go to the below link and install it in Firefox, it works perfectly. http://www.sephiroth.it/firefox/flashtracer/
If you need to see Flash trace output in Firefox, install this plugin:
http://www.sephiroth.it/firefox/flashtracer/
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