Filed by: csabou [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer?job_id=370800503&repo=mozilla-central
Full log: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/WqTdKiBiRUu6aJBCwJT-9A/runs/0/artifacts/public/logs/live_backing.log

[task 2022-03-12T22:19:55.243Z] 22:19:55     INFO - TEST-PASS | devtools/client/debugger/test/mochitest/browser_dbg-features-source-text-content.js | undefined assertion name - 
[task 2022-03-12T22:19:55.244Z] 22:19:55     INFO - Leaving test bound testFailingHtmlSource
[task 2022-03-12T22:19:55.244Z] 22:19:55     INFO - Entering test bound testLoadingHtmlSource
[task 2022-03-12T22:19:55.245Z] 22:19:55     INFO - Test loading progress of html page sources
[task 2022-03-12T22:19:55.245Z] 22:19:55     INFO - Adding a new tab with URL: http://localhost:35007/slow-loading-page.html
[task 2022-03-12T22:19:55.245Z] 22:19:55     INFO - Tab added and finished loading
[task 2022-03-12T22:19:55.246Z] 22:19:55     INFO - Opening the toolbox
[task 2022-03-12T22:19:55.247Z] 22:19:55     INFO - Buffered messages logged at 22:18:37
[task 2022-03-12T22:19:55.247Z] 22:19:55     INFO - Console message: [JavaScript Error: "Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”)." {file: "chrome" line: 511}]
[task 2022-03-12T22:19:55.248Z] 22:19:55     INFO - Console message: [JavaScript Error: "Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”)." {file: "chrome" line: 511}]
[task 2022-03-12T22:19:55.249Z] 22:19:55     INFO - Console message: [JavaScript Error: "Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”)." {file: "chrome" line: 62}]
[task 2022-03-12T22:19:55.249Z] 22:19:55     INFO - Buffered messages logged at 22:18:38
[task 2022-03-12T22:19:55.250Z] 22:19:55     INFO - Console message: [JavaScript Error: "Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”)." {file: "chrome" line: 511}]
[task 2022-03-12T22:19:55.250Z] 22:19:55     INFO - Console message: [JavaScript Error: "Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”)." {file: "chrome" line: 511}]
[task 2022-03-12T22:19:55.252Z] 22:19:55     INFO - Console message: [JavaScript Error: "Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”)." {file: "chrome" line: 62}]
[task 2022-03-12T22:19:55.252Z] 22:19:55     INFO - Console message: [JavaScript Warning: "Use of nsIFile in content process is deprecated." {file: "resource://gre/modules/NetUtil.jsm" line: 253}]
[task 2022-03-12T22:19:55.253Z] 22:19:55     INFO - Toolbox opened and focused
[task 2022-03-12T22:19:55.253Z] 22:19:55     INFO - Waiting on sources: slow-loading-page.html
[task 2022-03-12T22:19:55.254Z] 22:19:55     INFO - Waiting for state change: source slow-loading-page.html exists
[task 2022-03-12T22:19:55.254Z] 22:19:55     INFO - Buffered messages finished
[task 2022-03-12T22:19:55.254Z] 22:19:55     INFO - TEST-UNEXPECTED-FAIL | devtools/client/debugger/test/mochitest/browser_dbg-features-source-text-content.js | Test timed out - 
[task 2022-03-12T22:19:55.518Z] 22:19:55     INFO - Removing tab.
[task 2022-03-12T22:19:55.518Z] 22:19:55     INFO - Waiting for event: 'TabClose' on [object XULElement].
[task 2022-03-12T22:19:55.565Z] 22:19:55     INFO - Got event: 'TabClose' on [object XULElement].
[task 2022-03-12T22:19:55.587Z] 22:19:55     INFO - Tab removed and finished closing
[task 2022-03-12T22:19:55.640Z] 22:19:55     INFO - GECKO(1608) | JavaScript error: resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm, line 217: TypeError: can't access property "notifyTargetDestroyed", watcher is undefined
[task 2022-03-12T22:19:56.348Z] 22:19:56     INFO - Removing tab.
[task 2022-03-12T22:19:56.349Z] 22:19:56     INFO - Waiting for event: 'TabClose' on [object XULElement].
[task 2022-03-12T22:19:56.392Z] 22:19:56     INFO - Got event: 'TabClose' on [object XULElement].[task 2022-03-12T22:19:56.554Z] 22:19:56     INFO - Console message: [JavaScript Error: "TypeError: can't access property "notifyTargetDestroyed", watcher is undefined" {file: "resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm" line: 217}]
[task 2022-03-12T22:19:56.554Z] 22:19:56     INFO - receiveMessage@resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm:217:11
[task 2022-03-12T22:19:56.554Z] 22:19:56     INFO - 
[task 2022-03-12T22:19:56.559Z] 22:19:56     INFO - GECKO(1608) | JavaScript error: resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm, line 217: TypeError: can't access property "notifyTargetDestroyed", watcher is undefined
[task 2022-03-12T22:19:57.263Z] 22:19:57     INFO - Removing tab.
[task 2022-03-12T22:19:57.264Z] 22:19:57     INFO - Waiting for event: 'TabClose' on [object XULElement].
[task 2022-03-12T22:19:57.291Z] 22:19:57     INFO - Got event: 'TabClose' on [object XULElement].
[task 2022-03-12T22:19:57.316Z] 22:19:57     INFO - Tab removed and finished closing
[task 2022-03-12T22:19:57.399Z] 22:19:57     INFO - Console message: [JavaScript Error: "TypeError: can't access property "notifyTargetDestroyed", watcher is undefined" {file: "resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm" line: 217}]
[task 2022-03-12T22:19:57.399Z] 22:19:57     INFO - receiveMessage@resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm:217:11
[task 2022-03-12T22:19:57.399Z] 22:19:57     INFO - 
[task 2022-03-12T22:19:57.404Z] 22:19:57     INFO - GECKO(1608) | JavaScript error: resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm, line 217: TypeError: can't access property "notifyTargetDestroyed", watcher is undefined
[task 2022-03-12T22:19:58.165Z] 22:19:58     INFO - Removing tab.
[task 2022-03-12T22:19:58.167Z] 22:19:58     INFO - Waiting for event: 'TabClose' on [object XULElement].
[task 2022-03-12T22:19:58.186Z] 22:19:58     INFO - Got event: 'TabClose' on [object XULElement].
[task 2022-03-12T22:19:58.213Z] 22:19:58     INFO - Tab removed and finished closing
[task 2022-03-12T22:19:58.237Z] 22:19:58     INFO - Console message: [JavaScript Error: "TypeError: can't access property "notifyTargetDestroyed", watcher is undefined" {file: "resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm" line: 217}]
[task 2022-03-12T22:19:58.237Z] 22:19:58     INFO - receiveMessage@resource://devtools/server/connectors/js-window-actor/DevToolsFrameParent.jsm:217:11
[task 2022-03-12T22:19:58.237Z] 22:19:58     INFO - 
[task 2022-03-12T22:19:58.241Z] 22:19:58     INFO - GECKO(1608) | JavaScript error: , line 0: NotFoundError: No such JSWindowActor 'DevToolsFrame'
[task 2022-03-12T22:19:58.265Z] 22:19:58     INFO - Console message: [JavaScript Error: "NotFoundError: No such JSWindowActor 'DevToolsFrame'"]
[task 2022-03-12T22:19:58.268Z] 22:19:58     INFO - TEST-PASS | devtools/client/debugger/test/mochitest/browser_dbg-features-source-text-content.js | The main process DevToolsServer has no pending connection when the test ends - 
[task 2022-03-12T22:26:08.279Z] 22:26:08     INFO - Buffered messages finished
[task 2022-03-12T22:26:08.281Z] 22:26:08    ERROR - TEST-UNEXPECTED-TIMEOUT | devtools/client/debugger/test/mochitest/browser_dbg-features-source-text-content.js | application timed out after 370 seconds with no output
[task 2022-03-12T22:26:08.281Z] 22:26:08    ERROR - Force-terminating active process(es).

Alexandre, can this be a regression of bug 1754407?

Yes, this test has been added in bug 1754407.

But this timeout might be fixed by bug 1759146 or bug 1759224 (two other intermittents)