Bug: Intermittent browser/modules/test/browser/browser_ProcessHangNotifications.js | A promise chain failed to handle a rejection: can't access property "isAppProvided", engine is null - stack: _updateURLBarPlaceholder@chrome://browser/content/browser.js:4138:
Status: RESOLVED
Priority: P2
Resolution: FIXED
Created: 2021-01-05 17:15:34+00:00
Resolved: 2021-02-09 19:52:15+00:00

**Filed by:** rmaries [at] mozilla.com
**Parsed log:** https://treeherder.mozilla.org/logviewer?job_id=325859565&repo=autoland
**Full log:** https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/ScpTx_6MR7Srn8HyCLmRyA/runs/0/artifacts/public/logs/live_backing.log

---
```
[task 2021-01-05T16:36:29.163Z] 16:36:29     INFO - TEST-START | browser/modules/test/browser/browser_ProcessHangNotifications.js
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - TEST-PASS | browser/modules/test/browser/browser_ProcessHangNotifications.js | With no open windows, should have terminated script for script hang. - 
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - TEST-PASS | browser/modules/test/browser/browser_ProcessHangNotifications.js | With no open windows, should have terminated global for add-on hang. - 
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - Buffered messages finished
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - TEST-UNEXPECTED-FAIL | browser/modules/test/browser/browser_ProcessHangNotifications.js | A promise chain failed to handle a rejection: can't access property "isAppProvided", engine is null - stack: _updateURLBarPlaceholder@chrome://browser/content/browser.js:4138:9
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - _updateURLBarPlaceholderFromDefaultEngine@chrome://browser/content/browser.js:4114:10
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - Rejection date: Tue Jan 05 2021 16:36:29 GMT+0000 (Greenwich Mean Time) - false == true - JS frame :: resource://testing-common/PromiseTestUtils.jsm :: assertNoUncaughtRejections :: line 282
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - Stack trace:
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - resource://testing-common/PromiseTestUtils.jsm:assertNoUncaughtRejections:282
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - chrome://mochikit/content/browser-test.js:Tester_execTest/<:1100
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - Leaving test bound terminateNoWindows
[task 2021-01-05T16:36:30.406Z] 16:36:30     INFO - Entering test bound terminateClosedWindow
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - GECKO(1988) | [Parent 1988: Main Thread]: I/DocShellAndDOMWindowLeak ++DOCSHELL 0x1313a4400 == 14 [pid = 1988] [id = 62]
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - GECKO(1988) | [Parent 1988: Main Thread]: I/DocShellAndDOMWindowLeak ++DOMWINDOW == 27 (0x15cafc900) [pid = 1988] [serial = 127] [outer = 0x0]
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - GECKO(1988) | [Parent 1988: Main Thread]: I/DocShellAndDOMWindowLeak ++DOMWINDOW == 28 (0x1317be400) [pid = 1988] [serial = 128] [outer = 0x15cafc900]
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - GECKO(1988) | [Parent 1988, Main Thread] WARNING: NS_ENSURE_TRUE(uri) failed: file /builds/worker/checkouts/gecko/caps/BasePrincipal.cpp:1327
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - Console message: [JavaScript Error: "URL constructor: null is not a valid URL." {file: "resource:///modules/ProcessHangMonitor.jsm" line: 403}]
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - _recordTelemetryForReport@resource:///modules/ProcessHangMonitor.jsm:403:21
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - stopHang@resource:///modules/ProcessHangMonitor.jsm:163:14
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - stopAllHangs@resource:///modules/ProcessHangMonitor.jsm:343:12
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - updateWindows@resource:///modules/ProcessHangMonitor.jsm:478:12
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - reportHang@resource:///modules/ProcessHangMonitor.jsm:702:10
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - observe@resource:///modules/ProcessHangMonitor.jsm:258:14
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - terminateNoWindows/<@chrome://mochitests/content/browser/browser/modules/test/browser/browser_ProcessHangNotifications.js:435:18
[task 2021-01-05T16:36:30.409Z] 16:36:30     INFO - terminateNoWindows@chrome://mochitests/content/browser/browser/modules/test/browser/browser_ProcessHangNotifications.js:434:42```