See for example:

https://firefoxci.taskcluster-artifacts.net/aR7dx3AmQ_-BesR_WBncDQ/0/public/logs/live_backing.log

The last test to run:

[task 2020-01-07T00:34:27.872Z] 00:34:27     INFO - REFTEST TEST-PASS | file:///builds/worker/workspace/build/tests/reftest/tests/dom/media/test/crashtests/1526044.html | (LOAD ONLY)
[task 2020-01-07T00:34:27.873Z] 00:34:27     INFO - REFTEST TEST-END | file:///builds/worker/workspace/build/tests/reftest/tests/dom/media/test/crashtests/1526044.html

Followed by a lot of messages like this until the test runner kills the test suite.

[task 2020-01-07T00:34:27.936Z] 00:34:27     INFO - [Child 1245, Main Thread] WARNING: Trying to request nsIHttpChannel from DocumentChannelChild, this is likely broken: file /builds/worker/workspace/build/src/netwerk/ipc/DocumentChannelChild.cpp, line 63
[task 2020-01-07T00:34:27.972Z] 00:34:27     INFO - [Child 1245, Main Thread] WARNING: Trying to request nsIHttpChannel from DocumentChannelChild, this is likely broken: file /builds/worker/workspace/build/src/netwerk/ipc/DocumentChannelChild.cpp, line 63
[task 2020-01-07T00:34:28.089Z] 00:34:28     INFO - [Child 1245, Main Thread] WARNING: Trying to request nsIHttpChannel from DocumentChannelChild, this is likely broken: file /builds/worker/workspace/build/src/netwerk/ipc/DocumentChannelChild.cpp, line 63
[task 2020-01-07T00:34:28.090Z] 00:34:28     INFO - [Child 1245, Main Thread] WARNING: Trying to request nsIHttpChannel from DocumentChannelChild, this is likely broken: file /builds/worker/workspace/build/src/netwerk/ipc/DocumentChannelChild.cpp, line 63
[task 2020-01-07T00:34:28.091Z] 00:34:28     INFO - [Child 1245, Main Thread] WARNING: NS_ENSURE_TRUE(request) failed: file /builds/worker/workspace/build/src/netwerk/base/nsLoadGroup.cpp, line 574
[task 2020-01-07T00:34:28.108Z] 00:34:28     INFO - [Child 1245, Main Thread] WARNING: NS_ENSURE_TRUE(!mHasOrHasHadOwnerWindow || mOwnerWindow) failed: file /builds/worker/workspace/build/src/dom/events/DOMEventTargetHelper.cpp, line 321
[task 2020-01-07T00:34:28.109Z] 00:34:28     INFO - [Child 1245, Main Thread] WARNING: Inner window does not have active document.: file /builds/worker/workspace/build/src/dom/base/nsGlobalWindowInner.cpp, line 3338
[task 2020-01-07T00:34:28.205Z] 00:34:28     INFO - [Child 1245, Main Thread] WARNING: Trying to request nsIHttpChannel from DocumentChannelChild, this is likely broken: file /builds/worker/workspace/build/src/netwerk/ipc/DocumentChannelChild.cpp, line 63

Matt wdyt?