Central as beta simulation: https://treeherder.mozilla.org/#/jobs?repo=try&selectedJob=253917119&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel%2Crunnable&revision=05e1c33f877b884e4428c5ca8a4347bcf428fbdb&searchStr=%28remote%29

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=253917119&repo=try&lineNumber=1501

[task 2019-06-28T13:19:54.595Z] 13:19:54 INFO - TEST-PASS | remote/test/browser/browser_input_dispatchKeyEvent.js | The input caret has the correct index ("3"="3") -
[task 2019-06-28T13:19:54.595Z] 13:19:54 INFO - Send Left
[task 2019-06-28T13:19:54.599Z] 13:19:54 INFO - Send rawKeyDown for key ArrowLeft
[task 2019-06-28T13:19:54.600Z] 13:19:54 INFO - Send keyUp for key ArrowLeft
[task 2019-06-28T13:19:54.600Z] 13:19:54 INFO - Buffered messages finished
[task 2019-06-28T13:19:54.601Z] 13:19:54 INFO - TEST-UNEXPECTED-FAIL | remote/test/browser/browser_input_dispatchKeyEvent.js | Test timed out -
[task 2019-06-28T13:19:54.601Z] 13:19:54 INFO - GECKO(1080) | JavaScript error: resource://testing-common/PromiseTestUtils.jsm, line 110: uncaught exception: Object
[task 2019-06-28T13:19:54.601Z] 13:19:54 INFO - GECKO(1080) | MEMORY STAT | vsize 20974904MB | residentFast 1030MB
[task 2019-06-28T13:19:54.605Z] 13:19:54 INFO - TEST-OK | remote/test/browser/browser_input_dispatchKeyEvent.js | took 90180ms
[task 2019-06-28T13:19:54.606Z] 13:19:54 INFO - Not taking screenshot here: see the one that was previously logged
[task 2019-06-28T13:19:54.606Z] 13:19:54 INFO - TEST-UNEXPECTED-FAIL | remote/test/browser/browser_input_dispatchKeyEvent.js | Found a tab after previous test timed out: data:text/html;charset=utf-8,<input type=text> -
[task 2019-06-28T13:19:54.609Z] 13:19:54 INFO - checking window state
[task 2019-06-28T13:19:54.610Z] 13:19:54 INFO - Console message: [JavaScript Error: "uncaught exception: Object" {file: "resource://testing-common/PromiseTestUtils.jsm" line: 110}]
[task 2019-06-28T13:19:54.612Z] 13:19:54 INFO - TEST-START | remote/test/browser/browser_main_target.js

Julian, this seems to be regressed by Bug 1543142, can you please take a look at it?

Sure, thanks for the ping.

It seems that the test times out when we wait for the "selectionchange" event after simulating an arrowLeft.
It turns out that listening to selectionchange on input is behind the pref dom.select_events.textcontrols.enabled , which is Nightly only.

I will force the pref in the test, that should fix the issue.

The test was relying on selectionchange events fired on an input text element.
This event is behind a pref, flip the pref to true during the test in order to make it
pass on all channels

Importing the patch makes the failures go away:

Early Beta: https://treeherder.mozilla.org/#/jobs?repo=try&resultStatus=testfailed%2Cbusted%2Cexception&revision=24f4ab13539d9b779350817522c079779de84633

Late Beta: https://treeherder.mozilla.org/#/jobs?repo=try&resultStatus=testfailed%2Cbusted%2Cexception&revision=f26f9acf755459db69c03aeff65f8499f6180077

Julian, the patch seems to work, can we get this landed on tree and merged into m-c before tomorrow's merge into beta? Thank you.

I suppose I can land it without review since it's test only.
I don't see any other option since it's sunday.

https://hg.mozilla.org/mozilla-central/rev/adc59d50adf8

This is already on beta https://hg.mozilla.org/releases/mozilla-beta/rev/adc59d50adf815ad6764ff235f833a5ba74291b6 and the tests are green. https://treeherder.mozilla.org/#/jobs?repo=mozilla-beta&resultStatus=success%2Ctestfailed%2Cbusted%2Cexception&classifiedState=unclassified&revision=53ea74d2bd09de0972820d6264abf1e17c1f1a79&searchStr=remote