There is an extension available for both programs that will allow you to get a clickable link from any message to the POPFile UI. It will also allow you to display the X-Text-Classification header more easily. The extension is called mnenhy (short for mail-news ehancements) and can be found at mnenhy.mozdev.org.
Here's the road to clickable X-POPFile-Link headers:
That's it. When you now view a message in Mozilla or Thunderbird and choose to display the 'Extended Normal View' for the headers (and don't choose the 'Brief' mode), you will get a clickable link to the POPFile UI.
The method to do this is essentially the same as for the X-POPFile-Link header. When you add that header in mnenhy's configuration dialog, enter these values:
Should you find anything in the documentation that is incomplete, unclear, outdated or just plain wrong, please let us know and leave a note in the Documentation Forum.