Firefox 25 crashing on HTML5 video

[Bryon]

% uname -a
FreeBSD amnesiac 9.1-RELEASE-p7 FreeBSD 9.1-RELEASE-p7 #0: Mon Sep 9 
21:23:37 UTC 2013 
root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC i386

% ident /usr/ports/www/firefox/Makefile
/usr/ports/www/firefox/Makefile:
      $FreeBSD: www/firefox/Makefile 332422 2013-11-01 23:16:27Z flo $

Problem:
When I visit vimeo.com, attempt to play any video, firefox crashes and I 
get:

Assertion failed: (wrote >= 0 && wrote == got), function 
alsa_refill_stream, file 
/usr/ports/www/firefox/work/mozilla-release/media/libcubeb/src/cubeb_alsa.c, 
line 319.
Abort

No core dump, just abort and a crash. This also happens at many sites 
that have embedded audio feeds (soundcloud etc). Youtube works fine. 
Also, midori has no problems at all playing anything anywhere. Why would 
firefox be looking for anything in a port work directory?