I should clarify and say that I'm running a debugging build of XULRunner.  The SEGV happens for debug
builds because of a MOZ_ASSERT which is designed to catch bugs during the debug process rather than make
browsers crash in the field.  (I'm guessing that manipulating the clipboard was considered something
"internal" rather than external.)  Since conkeror touches these objects, it should DTRT with them.

(Downgrading from urgent.)