This seems more of an apache configuration problem, than something wrong with iceweasel. Apache isn't recognising the PHTML file as PHP. Since its not a valid extension.
You'll wna to add phtml to the extension for http something like this:
AddType application/x-httpd-php .php .php3 .phtml
in your httpd.conf will help. Look for where php is already added.
If your using apache2 check the /etc/apache2/mods-available/php5.conf and php5.load, and run "a2enmod php5" to make sure php is enabled.