firefox crash viewing video on CentOS 5.5

Anyone out there view non-flash video anymore?  :-)

Firefox / seamonkey crashes on CentOS 5.5 (we use x86_64, haven't tried
i386) when they encounter non-flash video files, e.g.,
http://www.nist.gov/itl/math/hpcvg/upload/vaneRheom_20101203_02.wmv  or
other videos at, for example,
<http://www.nist.gov/itl/math/hpcvg/concretemm.cfm>.  I've also tested
some other .avi's with no success.

This started happening about 6-8 weeks ago.  mplayer from the command
line plays the videos fine.

Can't quite put my finger on if it's gecko-mediaplayer or gmplayer.

I've got a bunch of debuginfo's installed, probably not all the needed
ones, but note that
http://dl.atrpms.net/debug/el5-x86_64/atrpms/stable/mplayer-debuginfo-1.0-78_snap20101002.el5.x86_64.rpm
is only 10KB in size and 'rpm -ql' reports no files.

gmplayer (part of mplayer package) dies on startup too.  Looks like a
smoking gun to me.