Change that to:
<!-- TMPL_VAR APPNAME_USER_FIRST_NAME -->
You mean <TMPL_VAR APPNAME_USER_FIRST_NAME> don't you? Or did I miss the secret stealth hide-your-tags-in-html-comments feature? :-)
You missed it: http://search.cpan.org/author/SAMTREGAR/HTML-Template-2.6/Template.pm#NOTES
- Perrin
