If you ever decided to use Uploadify jQuery plug-in you might have noticed problems with debugging remote PHP code that this plugin relies on. [...] Unfortunately setting this up will not work with Uploadify Flash version since calls to remote server side is not done inside browser but inside flash plugin. [...] Few months ago I found my self blindly debugging it again and remembered that I read somewhere that xdebug parameters can be sent via GET/POST too.

He takes advantage of this fact and appends the "XDEBUG_SESSION_START" and "XDEBUG_SESSION" values in the "scriptData" handler for the Uploadify call. The XDebug session is then started when the script executes and your IDE will receive the results.