Installation of Fedora to standard Debain Tomcat via deployment descriptor files (fedora.xml context description in /var/lib/tomcat7/conf/Catalina/localhost) doesn't set up the webapp directory in the way RISearchServlet (and probably other components) is expecting it. In particular the directory /ri (containing stylesheets) is missing.
However, the set up of RISearchServlet doesn't check for existence/accessibility of these files on initialization.
Part of the problem seems to be, that Trippi needs absolute File path to the stylesheet files, instead of resource URL (obtained by calling getResource).
Maybe connected to this issue: