If you'd like to try the following workaround to stop the warning,
Change /plugins/content/jfbccontent/jfbccontent.php on line 287
else if ($this->view == 'category' && $article->catid != null)
to
else if ($this->view == 'category' && isset($article->catid) && $article->catid != null)
I've only briefly tested this change, but don't see any side effects. I've added the issue to our tracker for the next bug fix release.
-Melissa