Okay, turns out this issue was related to tabulator in general - I have fixed
the issues i talked about in msg490, though. I wasn't able to reproduce DanC's
problem.
Firefox's accept headers need to be configured to accept 'applcation/rdf+xml'
and 'text/rdf+n3'. This can be done for now by going to about:config and
setting network.http.accept.default to include both. I can and will put in an
option to toggle this setting today.