See TB33449489Q. I have no idea what's going on here, esp. given lack of line numbers. :(
Interestingly we still see a small handful of these, 5 in the last week http://crash-stats.mozilla.com/report/list?query_search=signature&query_type=contains&query=nsHttpTransaction%3A%3A~nsHttpTransaction&date=&range_value=1&range_unit=weeks&do_query=1&signature=nsHttpTransaction%3A%3A~nsHttpTransaction%28%29 At least there are line numbers, but I'm not sure they help much.
All those crashes are 3.0.x. So yes, for some definitions of "still" ;)