Only on this slave, during startup of jobs run by the reftest harness (reftests, crashtests, jsreftests), something attempts to contact example.com either before the proxy of that to localhost is set up, or maybe it's only www.example.com that's proxied, not example.com, dunno. Either way, only this one slave is crashing on startup. Disabled.
Not just reftest harness, there was another, so it was probably just one of the many things like update checks and safebrowsing that we proxy to example.com, and this slave refusing to use the proxying. Chances are that just a reimage will cure it.
Back online and green jobs after been re-imaged.