Mysterious crash/freeze in X11 with newcons

I had two crashes, or more accurately, freezes, when web-browsing.

First was with Firefox on an easy National Weather Service page, I was scrolling down with down-arrow key, and system suddenly froze, no response to keyboard or mouse, display stayed (until I hit Reset). 

uname -a shows

FreeBSD amelia4 11.0-CURRENT FreeBSD 11.0-CURRENT #4 r264310: Thu Apr 10 06:56:03 UTC 2014     root_at_amelia4:/usr/obj/usr/src/sys/SANDY11NC  amd64

NC in kernel name is for NewCons, SC would be SysCons, and I compiled kernel both ways.

Second was with Midori, actually twice, on a more complex site, 1040now.net :

I checked /var/log/messages, and /var/log/messages.0.bz2, and noticed 

Apr 15 08:29:52 amelia4 kernel: error: [drm:pid806:drm_do_get_edid] *ERROR* VGA-1: EDID block 0 inva
lid.

and a few minutes later,

Apr 15 08:33:58 amelia4 kernel: error: [drm:pid806:drm_do_get_edid] *ERROR* VGA-1: EDID block 0 invalid.
Apr 15 08:33:58 amelia4 kernel: sysmouse: unknown ioctl: t:40007413
Apr 15 08:33:58 amelia4 kernel: sysmouse: unknown ioctl: t:40007413
Apr 15 08:33:58 amelia4 kernel: sysmouse: unknown ioctl: t:80007410

I notice from earlier, and think this must have been the crash with Firefox:

pr 14 23:09:18 amelia4 kernel: error: [drm:pid87853:drm_do_get_edid] *ERROR* VGA-1: EDID block 0 in
valid.
Apr 14 23:09:18 amelia4 kernel: sysmouse: unknown ioctl: t:40007413
Apr 14 23:09:18 amelia4 kernel: sysmouse: unknown ioctl: t:40007413
Apr 14 23:09:18 amelia4 kernel: sysmouse: unknown ioctl: t:80007410


I think these errors must have been the cause of the freeze/crash, and looking for somebody who recognizes what is *ERROR* VGA-1: EDID block 0 invalid.

Would I be better with syscons instead of newcons?  But then, how would I open a root window for such things as mounting and umounting disks/partitions, and anything else requiring root privilege?

Or would I do better on 10-stable?  But then if the problem is with the new Xorg, 10-stable would be no stabler than the bleeding-edge 11-head.

I am/was in window manager icewm-1.3.8 but think, since the problem occurred with both Firefox and Midori, the problem is with the new Xorg and possibly newcons rather than web browser.

Reason for building www/midori was to see if it would be safer than Firefox in terms of stability, and to compare bugs with Midori-0.5.5 on the System Rescue CD.

Tom