[Tracking Requested - why for this release]:
Central as Beta: https://treeherder.mozilla.org/#/jobs?repo=try&group_state=expanded&revision=a9116bffd43a99e4178fc73cc42135f703f07ac3&searchStr=wpt&selectedJob=282257106

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=282257106&repo=try&lineNumber=3807

[task 2019-12-21T13:30:02.516Z] 13:30:02 INFO - TEST-START | /fetch/api/abort/serviceworker-intercepted.https.html
[task 2019-12-21T13:30:02.517Z] 13:30:02 INFO - Clearing pref javascript.options.streams
[task 2019-12-21T13:30:02.533Z] 13:30:02 INFO - Setting pref javascript.options.streams (true)
[task 2019-12-21T13:30:02.534Z] 13:30:02 INFO - Closing window 37
[task 2019-12-21T13:30:12.942Z] 13:30:12 INFO -
[task 2019-12-21T13:30:12.942Z] 13:30:12 INFO - TEST-UNEXPECTED-TIMEOUT | /fetch/api/abort/serviceworker-intercepted.https.html | Already aborted request does not land in service worker - Test timed out
[task 2019-12-21T13:30:12.943Z] 13:30:12 INFO -
[task 2019-12-21T13:30:12.943Z] 13:30:12 INFO - TEST-UNEXPECTED-NOTRUN | /fetch/api/abort/serviceworker-intercepted.https.html | response.arrayBuffer() rejects if already aborted - expected PASS
[task 2019-12-21T13:30:12.943Z] 13:30:12 INFO -
[task 2019-12-21T13:30:12.944Z] 13:30:12 INFO - TEST-UNEXPECTED-NOTRUN | /fetch/api/abort/serviceworker-intercepted.https.html | response.blob() rejects if already aborted - expected PASS
[task 2019-12-21T13:30:12.944Z] 13:30:12 INFO -
[task 2019-12-21T13:30:12.944Z] 13:30:12 INFO - TEST-UNEXPECTED-NOTRUN | /fetch/api/abort/serviceworker-intercepted.https.html | response.formData() rejects if already aborted - expected PASS
[task 2019-12-21T13:30:12.945Z] 13:30:12 INFO -
[task 2019-12-21T13:30:12.945Z] 13:30:12 INFO - TEST-UNEXPECTED-NOTRUN | /fetch/api/abort/serviceworker-intercepted.https.html | response.json() rejects if already aborted - expected PASS
[task 2019-12-21T13:30:12.945Z] 13:30:12 INFO -
[task 2019-12-21T13:30:12.946Z] 13:30:12 INFO - TEST-UNEXPECTED-NOTRUN | /fetch/api/abort/serviceworker-intercepted.https.html | response.text() rejects if already aborted - expected PASS
[task 2019-12-21T13:30:12.946Z] 13:30:12 INFO -
[task 2019-12-21T13:30:12.947Z] 13:30:12 INFO - TEST-UNEXPECTED-NOTRUN | /fetch/api/abort/serviceworker-intercepted.https.html | Stream errors once aborted. - expected PASS
[task 2019-12-21T13:30:12.947Z] 13:30:12 INFO - TEST-UNEXPECTED-TIMEOUT | /fetch/api/abort/serviceworker-intercepted.https.html | expected OK
[task 2019-12-21T13:30:12.947Z] 13:30:12 INFO - TEST-INFO took 10427ms

Patch in bug 1588154 landed on autoland, we'll update the bugs once that is included in beta sims.

No longer occurs in beta sims after bug 1588154 landed:

https://treeherder.mozilla.org/#/jobs?repo=try&selectedJob=282645832&resultStatus=success%2Ctestfailed%2Cbusted%2Cexception%2Crunnable&revision=1ebb9b5fd35b03fbf546942033c54f2bb1eea4e9&searchStr=wpt%2C7&group_state=expanded

Verified fixed in latest beta sim:

https://treeherder.mozilla.org/#/jobs?repo=try&resultStatus=pending%2Crunning%2Ctestfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel%2Crunnable&revision=ec95a9b6fb3da934dca8dacc4b0f419658e09c8e&group_state=expanded