https://tbpl.mozilla.org/php/getParsedLog.php?id=8015969&tree=Mozilla-Inbound&full=1 includes a screenshot, showing that the mochitest harness tried to load "/tests/dom/tests/-ochitest/dom-level2-core/test_isSupported09.html" (the path is tests/mochitest, so that's full of wtf?), but more seriously also showing the Bluetooth Setup Assistant dialog complaining that it can't find a keyboard, and a dialog announcing that "Your computer was restarted because of a problem." making it the single best smoking gun screenshot I've ever seen in a log, even though it's sadly pointed at you rather than at a test.
Bluetooth is listed as "off" on this slave, so I'm not sure what's going on there.
Disabled in slavealloc for now.
reimage requested in bug 715605