Reproduced https://bugzilla.mozilla.org/show_bug.cgi?id=385095 Reproduced with 2.0.0.6 build from ports. Moving /usr/local/lib/thunderbird/defaults/isp/rss.rdf to /usr/local/lib/thunderbird/isp/rss.rdf in my local install works around the issue as described in the Bugzilla entry.