VirtualBox 4.3.20 breaks FreeBSD Xorg

I updated to VirtualBox v4.3.20 (host and guest additions)  and whenever I attempt to launch startx or startxfce4 on the guest I only see a blank black screen. The log file (/var/log/Xorg.0.log) showed that the issue was vboxvideo related.

[   407.864] (II) AIGLX: Screen 0 is not DRI2 capable
[   407.864] drmOpenDevice: node name is /dev/dri/card0
[   407.864] drmOpenDevice: open result is 13, (OK)
[   407.864] drmOpenByBusid: Searching for BusID pci:0000:00:02.0
[   407.864] drmOpenDevice: node name is /dev/dri/card0
[   407.864] drmOpenDevice: open result is 13, (OK)
[   407.864] drmOpenByBusid: drmOpenMinor returns 13
[   407.864] drmOpenByBusid: Interface 1.4 failed, trying 1.1
[   407.864] drmOpenByBusid: drmGetBusid reports pci:0000:00:02.0
[   407.865] (EE) AIGLX error: dlopen of /usr/local/lib/dri/vboxvideo_dri.so failed (Cannot open "/usr/local/lib/dri/vboxvideo_dri.so")

I downgraded VirtualBox to v4.3.18 and Xfce works again!