How do I create Growl notifications for FCE?
Did you save the script with the idle handler as a .app file with the "Stay Open" checkbox selected in the Save dialog?

This is required for the code within the idle handler to be run "on idle", else it won't run at all. Save it that way and try again.

You're checking windowList for missing value. This sounds like a condition where no FCE windows are open. If you want the block where you're scripting Growl to execute, it should be within the if statement, not after.

Also, depending on what version of Growl you're using, it might respond to one of "Growl" (v1.3+) or "GrowlHelperApp" (v&lt;1.3), but not the other. To future-proof your script, replace

tell application "GrowlHelperApp


with the following:

tell application id "com.Growl.GrowlHelperApp"


All versions of Growl respond to that.

The block of code you have that triggers Growl looks like you modified their example, and from your comments it sounds like that's working fine.