This comes from bug 1339568 comment 1. This might be benign and just noisy in the console... or indicate that we're sending data up to the parent too late or not listening to shutdown notifications properly: [task 2017-02-11T00:45:42.282168Z] 00:45:42 INFO - ###!!! [Child][MessageChannel] Error: (msgtype=0x4400FD,name=PContent::Msg_AccumulateChildKeyedHistogram) Closed channel: cannot send/recv [task 2017-02-11T00:45:42.283184Z] 00:45:42 INFO - [Child 5240] WARNING: MsgDropped in ContentChild: file /home/worker/workspace/build/src/dom/ipc/ContentChild.cpp, line 2049 [task 2017-02-11T00:45:42.283380Z] 00:45:42 INFO - [Child 5240] WARNING: '!contentChild->SendAccumulateChildKeyedHistogram(keyedAccumulationsToSend)', file /home/worker/workspace/build/src/toolkit/components/telemetry/TelemetryIPCAccumulator.cpp, line 215 [task 2017-02-11T00:45:44.284873Z] 00:45:44 INFO - ###!!! [Child][MessageChannel] Error: (msgtype=0x4400FD,name=PContent::Msg_AccumulateChildKeyedHistogram) Closed channel: cannot send/recv [task 2017-02-11T00:45:44.286157Z] 00:45:44 INFO - [Child 5240] WARNING: MsgDropped in ContentChild: file /home/worker/workspace/build/src/dom/ipc/ContentChild.cpp, line 2049 [task 2017-02-11T00:45:44.286317Z] 00:45:44 INFO - [Child 5240] WARNING: '!contentChild->SendAccumulateChildKeyedHistogram(keyedAccumulationsToSend)', file /home/worker/workspace/build/src/toolkit/components/telemetry/TelemetryIPCAccumulator.cpp, line 215

P2 for picking this up for an initial investigation in the next iteration.