I seem to not have follow instructions correctly, I guess. In any case, I am not getting a correct header.
I did as follows:
1. I made a new donottrack.js file by coping your updated code from your post. I put that in root\components folder.
2. I created donottrack.kmm file by copying your code. I put that in my user macro folder.
3. I created a donottrack.js file in root\defaults with the line to set the pref to 1.
The menu works, and my configuration file has the "navigator.doNotTrack" value as set by the last menu change. I have confirmed that the menu changes the value.
When I go here: http://browserspy.dk/donottrack.php
I get: No Do Not Track Header detected!
Did I misinterpret an instruction?