using default conf, cliking on exernal links does not do any thing. When adding urlCommand "firefox %s" to ~/.xpdfrc then I get external link in FireFox. Please insert similar suport directly in /etc/xpdfrc. To avoid forcing people to use special browser, Debian people have a special script to autodetect default browser, or make some calls to window manager ... any way, no suport of ext links at all is not nice IMHO. Good luck.
you are right there should be a default. I added your one, thanks.