Bug: Intermittent unknown test url | uncaught exception - NS_ERROR_XPC_BAD_CONVERT_JS: Could not convert JavaScript argument arg 0 [nsIObserverService.addObserver] at construct@chrome://global/content/elements/browser-custom-element.js:1034:24
Status: RESOLVED
Priority: P5
Resolution: INCOMPLETE
Created: 2023-07-08 14:45:36+00:00
Resolved: 2023-08-18 12:03:31+00:00

**Filed by:** smolnar [at] mozilla.com
**Parsed log:** https://treeherder.mozilla.org/logviewer?job_id=421985252&repo=autoland
**Full log:** https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/QtejBiz-RgaeMZ6gADMTZg/runs/0/artifacts/public/logs/live_backing.log

---
```
TEST-OK | browser/base/content/test/tabs/browser_multiselect_tabs_using_Shift.js | took 7140ms
[task 2023-07-08T14:04:58.629Z] 14:04:58    ERROR - GECKO(9504) | TEST-UNEXPECTED-FAIL | unknown test url | uncaught exception - NS_ERROR_XPC_BAD_CONVERT_JS: Could not convert JavaScript argument arg 0 [nsIObserverService.addObserver] at construct@chrome://global/content/elements/browser-custom-element.js:1034:24
[task 2023-07-08T14:04:58.630Z] 14:04:58     INFO - GECKO(9504) | connectedCallback@chrome://global/content/elements/browser-custom-element.js:330:12
[task 2023-07-08T14:04:58.631Z] 14:04:58     INFO - GECKO(9504) | _insertBrowser@chrome://browser/content/tabbrowser.js:2380:24
[task 2023-07-08T14:04:58.633Z] 14:04:58     INFO - GECKO(9504) | addTab@chrome://browser/content/tabbrowser.js:2780:16
[task 2023-07-08T14:04:58.635Z] 14:04:58     INFO - GECKO(9504) | Tester_waitForWindowsState@chrome://mochikit/content/browser-test.js:460:16
[task 2023-07-08T14:04:58.637Z] 14:04:58     INFO - GECKO(9504) | nextTest@chrome://mochikit/content/browser-test.js:1007:10
[task 2023-07-08T14:04:58.638Z] 14:04:58     INFO - GECKO(9504) | async*testScope/test_finish/<@chrome://mochikit/content/browser-test.js:1794:25
[task 2023-07-08T14:04:58.648Z] 14:04:58     INFO - GECKO(9504) | run@chrome://mochikit/content/browser-test.js:1714:9
[task 2023-07-08T14:04:58.649Z] 14:04:58     INFO - GECKO(9504) | JavaScript error: chrome://global/content/elements/browser-custom-element.js, line 1034: NS_ERROR_XPC_BAD_CONVERT_JS: Could not convert JavaScript argument arg 0 [nsIObserverService.addObserver]
[task 2023-07-08T14:04:58.650Z] 14:04:58     INFO - checking window state
[task 2023-07-08T14:04:58.680Z] 14:04:58     INFO - Console message: [JavaScript Error: "NS_ERROR_XPC_BAD_CONVERT_JS: Could not convert JavaScript argument arg 0 [nsIObserverService.addObserver]" {file: "chrome://global/content/elements/browser-custom-element.js" line: 1034}]
[task 2023-07-08T14:04:58.681Z] 14:04:58     INFO - construct@chrome://global/content/elements/browser-custom-element.js:1034:24
[task 2023-07-08T14:04:58.681Z] 14:04:58     INFO - connectedCallback@chrome://global/content/elements/browser-custom-element.js:330:12
[task 2023-07-08T14:04:58.681Z] 14:04:58     INFO - _insertBrowser@chrome://browser/content/tabbrowser.js:2380:24
[task 2023-07-08T14:04:58.681Z] 14:04:58     INFO - addTab@chrome://browser/content/tabbrowser.js:2780:16
[task 2023-07-08T14:04:58.682Z] 14:04:58     INFO - Tester_waitForWindowsState@chrome://mochikit/content/browser-test.js:460:16
[task 2023-07-08T14:04:58.682Z] 14:04:58     INFO - nextTest@chrome://mochikit/content/browser-test.js:1007:10
[task 2023-07-08T14:04:58.683Z] 14:04:58     INFO - async*testScope/test_finish/<@chrome://mochikit/content/browser-test.js:1794:25
[task 2023-07-08T14:04:58.683Z] 14:04:58     INFO - run@chrome://mochikit/content/browser-test.js:1714:9
[task 2023-07-08T14:04:58.683Z] 14:04:58     INFO - 
[task 2023-07-08T14:04:58.686Z] 14:04:58     INFO - TEST-START | browser/base/content/test/tabs/browser_multiselect_tabs_using_Shift_and_Ctrl.js
```